Technique and Application of a Non-Invasive Three Dimensional Image
Matching Method for the Study of Total Shoulder Arthroplasty
by
Daniel Frank Massimini
B.S., Mechanical Engineering
University of California at Los Angeles (UCLA), 2005
Submitted to the Department of Mechanical Engineering
in Partial Fulfillment of the Requirements for the Degree of
Master of Science in Mechanical Engineering
at the
Massachusetts Institute of Technology
February 2009
© 2009 Massachusetts Institute of Technology
All rights reserved
Signature of Author .......................................................................................................
Department of Mechanical Engineering
December 19, 2008
Certified by ....................................................................................................................
Guoan Li, PhD
Associate Professor of Orthopaedic Surgery
Harvard Medical School
Thesis Supervisor
Certified by ....................................................................................................................
Derek Rowell, PhD
Professor of Mechanical Engineering
Thesis Supervisor
Accepted by ..................................................................................................................
David E. Hardt, PhD
Professor of Mechanical Engineering
Chairman, Department Committee on Graduate Students
1
2
Technique and Application of a Non-Invasive Three Dimensional Image
Matching Method for the Study of Total Shoulder Arthroplasty
by
Daniel Frank Massimini
Submitted to the Department of Mechanical Engineering
on December 19, 2008 in Partial Fulfillment of the
Requirements for the Degree of
Master of Science in Mechanical Engineering
Abstract
Knowledge of in-vivo glenohumeral joint biomechanics after total shoulder
arthroplasty are important for the improvement of patient function, implant longevity
and surgical technique. No data has been published on the in-vivo glenohumeral
joint contact locations in patients after total shoulder arthroplasty. Therefore, the
objectives of this thesis were to determine the in-vivo glenohumeral joint contact
locations and humeral head translations in patients after total shoulder arthroplasty.
First, a non-invasive three dimensional fluoroscopic image matching method
was developed and validated for use in the shoulder joint complex. Next, a group of
patients that have undergone clinically successful total shoulder arthroplasty
surgeries were recruited for study and imaged by the fluoroscopic imaging technique.
The fluoroscopic imaging system was recreated in a virtual environment and the invivo kinematics that were recorded by the fluoroscopes were recreated with three
dimensional models. The contact centroids of the glenohumeral joint and humeral
head translations were measured using solid modeling software.
In summary, this thesis quantified the in-vivo glenohumeral joint contact
locations and humeral head translations after total shoulder arthroplasty. These data
provides surgeons and engineers valuable information for developing surgical
treatments that may better help recreate ‘normal’ motion of the shoulder after total
shoulder arthroplasty.
Thesis Supervisor: Guoan Li, PhD
Title: Associate Professor of Orthopaedic Surgery
Harvard Medical School
3
4
Acknowledgements
As I look back on the last three years of my life that I have lived in Boston, I
often wonder where all my time has gone. There is so much to see and do in this
city, yet I feel that I have seen and done so little. As I begin my fourth year at MIT, I
realize that I will never get to be a tourist in the city that I now call home. Life just
continues to snowball faster and faster at an unprecedented velocity that I never
imagined possible. Although this is not to say that I haven’t thoroughly enjoyed my
time as a graduate student at MIT, albeit filled with many ups and downs along the
way.
Yet looking back, I would not have done anything differently.
In between
juggling classes, research, president of Snowriders (06-07), organizing two graduate
student ski trips (07 & 08), getting food for various G.A.M.E events, making new
friends and living life to the fullest, I would say that I have had my hands full.
However, without the following (truncated list due to space limitations, although not
forgotten) people in my life, my journey at MIT thus far would not have been possible.
First, I must thank God for making this whole reality possible, for every detail
that He planned for my existence and for the amazing abilities that I was given. Next,
I would like to thank my adviser Dr. Guoan Li, for always believing in my abilities, for
standing up for me, for his patience and for being a mentor and a friend. Without his
belief and the support of his MGH Bioengineering Lab, I would not have had this
amazing opportunity. To Dr. Jon Warner, for all his clinical insight of the shoulder
joint complex and for making my research possible. To Dr. Derek Rowell for advising
my academic choices at MIT and for always confusing me with some guy named
5
Mike. I am glad we can both laugh about it. Additionally, I would like to thank each
and every member of the MGH Bioengineering Lab both past and present for his or
her contribution to my life. I would also like to thank Leslie Regan and Joan Kravit in
the Mechanical Engineering Graduate Office and Laurie Ward for all her help making
Snowriders so successful.
Also, I thank my family for understanding my decision to uproot and move
across the country from sunny southern California to snowy cold Boston to pursue a
graduate degree from MIT. Boston isn’t that cold after all. To my Dad for not getting
too angry when I drilled holes (age: three) in his shop floor and for not putting tools
back (age: current) in their assigned location. To my Mom for sending me care
packages of soap, toothpaste and dental floss because for some strange reason
these items are not available on the East Coast. To my sister Leanna and brother
Joseph for maintaining an incredibly close relationship even though we are so far
away. To all my aunts, uncles, cousins, relatives and grandparents, I thank you so
much for caring and loving me.
Finally, I thank Sarah for dragging me to the library on weekends to compose
this thesis. For all her understanding, patience and ability to motivate, I am forever
grateful. I cherish the time we have spent together and look forward to the time I
hope to share.
With humbleness and gratitude,
~Daniel
6
Contents
Acknowledgements .................................................................................................. 5
Contents ....................................................................................................................7
List of Figures ........................................................................................................... 9
List of Tables ........................................................................................................... 13
Chapter 1 ................................................................................................................. 15
1.1 Introduction...................................................................................................... 15
1.2 Shoulder Overview .......................................................................................... 17
1.3 Previous Research .......................................................................................... 23
1.4 Conclusion - Why This Research Was Done................................................... 25
1.5 Related Publication & Conferences ................................................................. 26
Chapter 2 ................................................................................................................. 27
2.1 Non-Invasive Image Matching Method ............................................................ 27
2.2 Dual [plane] Fluoroscopic Imaging System (DFIS) .......................................... 29
2.3 Image Correction & Segmentation................................................................... 32
2.4 Virtual DFIS Environment & Matching ............................................................. 35
2.5 Accuracy & Repeatability................................................................................. 38
2.6 Contact & Validation ........................................................................................ 40
Chapter 3 ................................................................................................................. 45
3.1 In-Vivo Shoulder Kinematics: Application of Technique .................................. 45
3.2 Total Shoulder Arthroplasty - Study Design..................................................... 46
3.3 Glenohumeral Contact Results........................................................................ 51
7
3.4 Humeral Head Kinematics Results .................................................................. 56
3.5 Coupled Motion ............................................................................................... 60
3.6 Discussion - Comparison With Previous Results............................................. 62
Chapter 4 ................................................................................................................. 69
4.1 Discourse......................................................................................................... 69
4.2 Advantages & Limitations ................................................................................ 70
4.3 Future Work..................................................................................................... 72
4.3.1 Dynamic Scapulothoracic Kinematics After TSA....................................... 73
4.3.2 Dynamic Shoulder Kinematics - Validation of DFIS .................................. 79
4.3.3 Mini Grant Proposal For Anterior Stability ................................................. 84
4.4 Summary ......................................................................................................... 88
Appendix A - MATLAB© Files ................................................................................ 91
A.1 circlescentroid.rvb ........................................................................................... 91
A.2 surfacetocurve.rvb........................................................................................... 95
A.3 edgetosurface.rvb ........................................................................................... 96
References............................................................................................................... 99
8
List of Figures
Figure 1 The intercalated joints of the shoulder complex. ......................................... 17
Figure 2 Typical total shoulder arthroplasty components. ......................................... 18
Figure 3 Natural articular surface of the glenoid. ...................................................... 19
Figure 4 Glenoid surface........................................................................................... 20
Figure 5 Humeral head radius of curvature............................................................... 20
Figure 6 Static restraints of the shoulder joint complex............................................. 21
Figure 7 The muscles of the rotator cuff.................................................................... 22
Figure 8 Dual plane fluoroscopic imaging system shown with a subject in the central
viewing volume with the shoulder in 90° abduction with maximum external
rotation..................................................................................................... 29
Figure 9 Custom switch unit built to operate two fluoroscopes simultaneously with a
single input from the operator. Red and black buttons toggle high and low
radiation dosage, respectively. ................................................................ 30
Figure 10 Typical fluoroscopic image of the shoulder with TSA. ............................... 31
Figure 11 Typical fluoroscopic image of copper distortion correction plate. .............. 32
Figure 12 The actual holes in the copper plate are shown as blue diamonds. The
distorted holes as imaged by the fluoroscope are shown as pink triangles.
The pink triangles will be mapped to the blue diamonds using a
polynomial expression. (Units in millimeters) .......................................... 33
Figure 13 Typical fluoroscopic image of the shoulder with TSA after being
automatically segmented and manually adjusted for ancillary outlines.... 34
Figure 14 Virtual DFIS recreated in computer space from the geometry of the actual
fluoroscopic system, shown with CAD models of total shoulder
arthroplasty. ............................................................................................. 35
Figure 15 Left scapula shown with glenoid component. Cartesian coordinate system
is created with the origin at the geometric center of the component. ....... 36
9
Figure 16 Contact validation setup with robotic manipulation device. ...................... 41
Figure 17 Silicon rubber impression......................................................................... 42
Figure 18 MicroScribe® digitizer. ............................................................................. 42
Figure 19 The overlap area of the humeral head and glenoid component is shown in
pink. The black point is the centroid of the pink contact area. ................ 43
Figure 20 Digitized voided silicon area on the glenoid component. ......................... 43
Figure 21 Unscaled patient specific contact locations on the glenoid surface as a
function of arm position, shown by color code. All right shoulder contact
locations were mirrored to left glenoid components................................. 51
Figure 22 Percent occupancy per quadrant to all shoulder positions imaged. ......... 55
Figure 23 Discrete frequency of quadrant contact per shoulder position imaged..... 55
Figure 24 Unscaled patient humeral head center locations on the glenoid surface as
a function of arm position, shown by color code. All right shoulder
humeral head centers locations were mirrored to left glenoid components.
................................................................................................................. 56
Figure 25 Unscaled patient specific glenoid contact locations and humeral head
center locations on the glenoid articular surface as a function of arm
position, shown by color code. All right shoulder locations were mirrored
to left glenoid components. ...................................................................... 60
Figure 26 Plot of the glenoid contact centroid translation versus the humeral head
center translation, showing the ratio of glenohumeral contact translation to
the humeral head in X and Y directions. .................................................. 61
Figure 27 A virtual dual plane fluoroscopic imaging system with TSA components in
an abduction / adduction animation sequence. The cycle begins in the top
image with a humeral abduction of 28° to the vertical, peaks in the third
image at 55° and ends with the bottom image at 23°............................... 75
Figure 28 Axes definition of the glenoid with respect to a left shoulder complex
shown on the white glenoid. The complex motion path of the glenoid in
abduction and adduction over one test cycle is shown by the blue glenoid.
................................................................................................................. 76
10
Figure 29 Euler angular rotations of the glenoid normalized to the initial position and
humeral abduction / adduction relative to the vertical versus the cycle
time. Error bars not shown because they are too small to clearly render.
................................................................................................................. 77
Figure 30 Scapular rotation about the glenoid midline (Y axis) versus abduction /
adduction of the humerus relative to the vertical in the plane of the
scapula. Hysteresis is exhibited between the transition from abduction to
adduction. ................................................................................................ 77
Figure 31 Cadaver rigidly mounted to a custom built fixture allowing the shoulder to
freely move without obstruction. DFIS shown in image capture geometry.
................................................................................................................. 80
Figure 32 Virtual DFIS created in computer space from the actual geometry of the
fluoroscopes shown with 3D model of the scapula and humerus. ........... 81
Figure 33 Humerus abduction angle as a function of cycle time. The humerus
abduction axis is approximately collinear with the longitudinal axis of the
humeral shaft. .......................................................................................... 82
Figure 34 Scapula protraction/retraction translation as a function of cycle time in
approximately the coronal plane. ............................................................. 83
Figure 35 Three dimensional model of the shoulder joint, showing the scapula and
humerus bones. ....................................................................................... 85
11
12
List of Tables
Table 1 The mean and standard deviations reported for fifteen independent trials of
matching the glenoid and humeral head components. ............................... 39
Table 2 Delta X and Delta Y, respectively are the difference between the calculated
centroid of contact and the measured centroid using the silicon rubber
technique. SD Fluoro X and SD Fluoro Y, respectively are the repeatability
of locating the centroid when independently matching the glenoid and
humeral components within the virtual fluoroscopic imaging system. ........ 44
Table 3 The locations of the glenohumeral contact on the glenoid surface. The data
is not scaled for component size. Data presentation is made consistent by
mirroring all right shoulders to left glenoid components. ............................ 53
Table 4 Radial distance of the contact centroid from the center of the glenoid
component. Data is not scaled for glenoid component size. ..................... 54
Table 5 The locations of the humeral head center on the glenoid surface. The data
is not scaled for component size. Data presentation is made consistent by
mirroring all right shoulders to left glenoid components. ............................ 58
Table 6 Radial distance of the center of the humeral head from the center of the
glenoid component. Data is not scaled for glenoid component size. ......... 59
Table 7 Translation and rotation error observed between model and marker ‘gold
standard’ based tracking technique for fast and slow abduction speeds in
6DOF: 3 translations and 3 rotations. Values are reported as Average ±
Standard Deviation..................................................................................... 82
13
14
Chapter 1
1.1 Introduction
Total shoulder arthroplasty (TSA) has become a popular clinical choice for the
treatment of end-stage shoulder degeneration for a restoration of range-of-motion
(ROM) and pain relief1. The term arthroplasty refers to the surgical removal and
replacement of degenerative articular cartilage surfaces with engineered materials to
substitute for the body’s natural joint structures. Current TSA involves the surgical
visualization of the humeral head and glenoid articular surface in order to remove the
damaged structures with a bone saw and be replaced with a polyethylene glenoid
component and cobalt chromium humeral head. Dr. Charles Neer II first pioneered
this technique in 1953, when he created the first ‘monoblock’ design at the ColumbiaPresbyterian Medical Center at Columbia University2. Since that time, numerous
component designs and surgical techniques have been introduced to the market,
each with varying degrees of clinical success and acceptance. Surgical techniques
have evolved from simply making due with the implants available to careful balancing
of soft tissues around the anatomic components with minimally invasive surgeries.
The wide variety of available shoulder implant designs has primarily focused on
material selection, fixation features, anatomic sizing and most recently recreation of
the anatomic geometry of the healthy glenohumeral joint. Needless to say, these
advancements are only as capable as the surgeon performing the operation.
Numerous component failures such as component loosening and polyethylene
damage have been reported after implantation3-7. Several current case studies3, 8, 9
15
have sought to correlate complication rates, range of motion, subjective shoulder
values (SSV) and pain scores with surgical technique, rehabilitation protocol and the
number of TSA operations performed by a surgeon per year.
However, the
quantitative factors that influence these patient outcomes and affect the performance
of TSA in-vivo are fairly limited. No data has been reported on the glenohumeral joint
articular contact locations or humeral head translations in patients following TSA.
Such contact kinematic data are necessary for the improvement of implant designs
and surgical implantation technique; and ultimately to enhance component longevity.
Therefore, the purpose of this research was to validate a non-invasive imaging
technique and investigate the glenohumeral articular contact locations and humeral
head translations after anatomic TSA during active in-vivo shoulder abduction with
neutral, internal and external rotations using a novel dual plane fluoroscopic image
matching technique.
16
1.2 Shoulder Overview
The shoulder joint complex has the greatest ROM and is the least constrained
joint within the human body.
It is comprised of four separate joints, the
acromioclavicular, the sternoclavicular, the scapulothoracic, and the glenohumeral
joint (Fig 1). The two primary joints that contribute to the ROM and stability of the
Figure 1 The intercalated joints of the shoulder complex.
shoulder joint complex are the scapulothoracic and the glenohumeral joints. The
scapulothoracic joint is the tethering of the scapula to the thoracic rib cage by the
serratus anterior muscle and interdigitated fascia. The smooth gliding motion of the
scapula bone on the thoracic ribs results from contraction and relaxation of the
serratus anterior muscle and the elasticity of interdigitated fascia sandwiched
17
between the bones. On the other hand, the glenohumeral joint is a diarthrodial joint
where opposing bone surfaces of the glenoid and humeral head are covered in
Figure 2 Typical total shoulder arthroplasty components.
hyaline articular cartilage such that the bones of the scapula and humerus directly
interact with one another transmitting forces through the cartilage layer.
Osteoarthritis (OA) is the progressive degenerative breakdown of the hyaline articular
cartilage within a joint that causes bone-on-bone contact.
This bone-on-bone
contact is incredibly painful and causes many individuals to minimize their use of the
affected joint, such that, in extreme cases the pain is so severe that the individual
cannot use the joint at all.
In these extreme cases a total joint replacement
(arthroplasty) may help restore range-of-motion and relieve pain. Dr. Charles Neer II
pioneered total shoulder arthroplasty in 1953, when he created the first ‘monoblock’
design at the Columbia-Presbyterian Medical Center at Columbia University2.
18
Parsons 1998
Figure 3 Natural articular surface of the glenoid.
Total shoulder arthroplasty consists of replacing the native articular cartilage of the
glenoid and the humeral head with a polyethylene glenoid component and polished
cobalt chromium humeral head component (Fig 2). The glenoid component is made
from ultra high molecular weight polyethylene and is shaped to mimic the natural
glenoid (Fig 3). The natural glenoid excluding the labrum is on average 39±3.7mm
(30-48mm) in the superior-inferior direction, 23±2.7mm (18-30mm) in the anteriorposterior direction in the superior half and 29±3.1mm (21-35mm) in the anteriorposterior direction in the inferior half of the glenoid10 (Fig 4). The articular area11
(Parsons I.M IV 1998 Lecture Presentation Notes, University of Pittsburgh) is 800850 mm^2 with an average articular radius10-12 of curvature of 27.2 ±1.6mm and a
bony radius of curvature of 33.4±3.4mm. The humeral head component is made
19
from polished cobalt chromium and is spherically shaped like the natural humeral
head that has a uniform layer of articular cartilage. The articular surface area of the
humeral head is approximately three times greater than the articular surface area of
the glenoid. The radius of bony curvature10-12 of the humeral head is on average
25.2±0.7mm and the radius of articular curvature is 25.5±1.5mm (Fig 5). The smaller
radius of curvature of the humeral head to that of the glenoid is defined as the radial
mismatch and is important for allowing the humeral head to translate and rotate on
the glenoid articular surface4, 5, 13.
Figure 4 Glenoid surface.
Figure 5 Humeral head radius of curvature.
The stability of the shoulder joint is a compromise between static and dynamic
restraints14,
15
. The static restraints being the superior glenohumeral ligament, the
medial glenohumeral ligament, the anterior and posterior bands of the inferior
glenohumeral ligament, the axillary pouch of the inferior glenohumeral ligament, the
posterior capsule, the biceps tendon, the labrum and the articular cartilage (Fig 6).
20
Biceps Tendon
Posterior Capsule
SGHL
Cartilage
Labrum
MGHL
PB-IGHL
AB-IGHL
Axillary Pouch-IGHL
Figure 6 Static restraints of the shoulder joint complex.
The function of the ligaments is to limit excess translation and rotation of the humeral
head on the glenoid surface at the extreme ranges of motion14,
16
. The dynamic
restraints are the muscles of the rotator cuff, which are the infraspinatus,
supraspinatus, subscapularis and teres minor (Fig 7). Together the combined forces
generated by these muscles compress the humeral head into the glenoid cavity
creating a compressive stabilizing effect14,
17
.
Damage to these muscles can
severely limit the function and stability of the shoulder joint. In the healthy shoulder,
proper balance between agonist and antagonist rotator cuff muscles provide dynamic
stability, such that in a total shoulder replacement surgery, the surgeon must properly
tension these muscles after resecting their insertions to implant the components.
21
Figure 7 The muscles of the rotator cuff.
Thus a successful total shoulder arthroplasty operation serves not only to reduce
pain by replacing the damaged articular cartilage surfaces with engineered implants,
but helps restores ROM by restoring balance to the rotator cuff muscles that
degenerate over time.
22
1.3 Previous Research
Prior knowledge of TSA can be categorized as retrospective clinical reports,
in-vitro laboratory experiments, computational studies and in-vivo patient analysis.
Each of these research designs are not without their advantages and limitations, first
and foremost, in-vivo patient analysis is the only method to capture data with
functional muscle loads. Clinical reports have shown component failure, such as
glenoid component loosening and polyethylene damage after implantation3-7.
Several current case studies3, 8, 9 have sought to correlate complication rates, range
of motion, subjective shoulder values (SSV) and pain scores with surgical technique,
rehabilitation protocol and the number of TSA operations performed by a surgeon per
year. In-vitro cadaveric experiments16-23, albeit limited in muscle loading schemes,
have isolated geometric and soft tissue factors that affect the amount of translation
and rotation of the humeral head relative to the glenoid surface.
These in-vitro
studies have reveled that a wide range of normal glenohumeral translations
23-28
could exist in the healthy population.
radiographic
4, 31
and laboratory
5, 32, 33
12, 17, 19,
Computational finite element13,
29, 30
,
studies have highlighted the importance of
glenohumeral radial mismatch on glenoid loosening. Finite element and laboratory
studies have also provided theoretical values for TSA glenohumeral translations and
force transmission into the glenoid surface6, 13, 29, 30, 32, 34, 35. Glenoid retrieval studies
have helped to create a classification system for damage mechanisms of the
polyethylene component while identifying locations on the glenoid surface that
experience a greater degree of damage in-vivo6,
23
7, 36, 37
.
Bergmann et al. have
developed an instrumented shoulder prosthesis38 to measure the in-vivo dynamic
loads, but not location, experienced by the glenohumeral joint during functional
activities such as combing ones hair. The in-vivo translations of the center of the
humeral head relative to the glenoid fossa have been reported using several
techniques26, 31, 39-41. However, no data has been reported on the glenohumeral joint
articular contact locations and humeral head translations in patients following TSA.
24
1.4 Conclusion - Why This Research Was Done
Total shoulder arthroplasty has become the gold standard for restoring ROM
and pain relief in degenerative shoulder disease. However, accurate knowledge of
in-vivo shoulder kinematics still eludes orthopaedists and researchers. Accurate invivo kinematics is the foundation for relative motion between bones, contact patterns
of articular surfaces and boundary conditions for finite element and inverse dynamic
studies.
These data provide orthopaedists and bioengineers a quantitative
assessment of normal shoulder motion and the tools which to understand the efficacy
that various surgical modalities have on restoring shoulder pathologies. To date, no
data has been reported on the glenohumeral joint articular contact locations or
humeral head translations in patients following TSA. Contact locations in patients
following TSA could be compared to healthy shoulders to determine if normal contact
kinematics are restored following surgical reconstruction. Such contact kinematic
data are necessary for the improvement of implant designs and surgical implantation
technique; and ultimately to enhance component longevity. These data combined
with humeral head translations provide in-vivo parameters for wear simulators of the
polyethylene glenoid component and a basis which to compare damage modes of
failed glenoid components.
Thus, quantitatively measuring in-vivo shoulder
kinematics would open new doors in the field of shoulder biomechanics. Therefore,
the purpose of this research was to investigate the glenohumeral articular contact
locations and humeral head translations after anatomic TSA during dynamically
stabilized in-vivo shoulder abduction with neutral, internal and external rotations
using a novel dual plane fluoroscopic imaging technique.
25
1.5 Related Publication & Conferences
Manuscripts
1. “Glenohumeral Contact Kinematics In Patients After Total Shoulder Arthroplasty”
Daniel F Massimini, Jon JP Warner, Guoan Li (Submitted to JBJS: American)
2. “Humeral Head Translations: Greater Than Previously Thought – A Study in Total
Shoulder Arthroplasty” Daniel F Massimini, Jon JP Warner, Guoan Li (Draft in
Progress)
Posters, Abstracts & Talks
1. “Patient Specific In-Vivo Shoulder Contact Kinematics After Total Shoulder
Arthroplasty” Massimini DF, Li G, Warner JP (53rd ORS Annual Meeting 2007, Poster
and Podium)
2. “Validation of a Non-Invasive Measurement of Glenohumeral Articular Surface
Contact After TSA Utilizing a Silicon Rubber Technique” Massimini DF, Li G, Warner
JP (54th ORS Annual Meeting 2008, Poster)
3. “Glenohumeral Articular Contact Kinematics of Patients After Total Shoulder
Arthroplasty” Massimini DF, Li G, Warner JP (54th ORS Annual Meeting 2008,
Poster)
4. “Dynamic Scapular Motions of the Shoulder After Total Shoulder Arthroplasty
Using an Imaging Technique” Massimini DF, Li G, Warner JP (54th ORS Annual
Meeting 2008, Poster)
5. “Dynamic In-Vivo Scapular Motion in Abduction and Adduction” Massimini DF,
Warner JP, Li G (ASME Summer Biomechanics Conference, June 2008, Poster)
6. “In-Vivo Shoulder Contact Kinematics After Anatomic Total Shoulder Arthroplasty”
Massimini DF, Li G, Warner JP (76th AAOS Annual Meeting 2009, Podium)
26
Chapter 2
2.1 Non-Invasive Image Matching Method
The concept of image matching is relatively straightforward.
A 2D planer
image or picture of an object is taken and the spatial 3D orientation of the object is
recreated or matched by viewing the object from the perspective of the camera to the
image plane and adjusting its position until the projected silhouette overlaps the
object’s contours on the planer image. By matching multiple objects in the image
plane, it is possible to determine the relative position of the objects in spatial
coordinates. This technique assumes the knowledge of the distance between the
camera and image plane and the acquisition of accurate 3D models of the objects in
question.
Accurate models may be obtained by coordinate measuring machines
(CMM), laser scanning tools, advanced medical imaging techniques such as MRI and
CT and directly from Computer Aided Design (CAD) drawings. However, the single
image plane method described above suffers from out-of-plane accuracy, which is
the inability to determine the true distance of the object from the image plane, but can
be improved upon by using two simultaneous image planes. In essence, the second
image plane’s in-plane accuracy becomes the out-of-plane accuracy of the first
image plane.
Thus, this dual plane image matching technique lends itself to studying the
bones and implants within the human body to analyze the kinematics of various
27
joints. However, to look at the bones and implants within the human body, x-rays or
fluoroscopic images need to be used in place of standard photographs. First, a joint
of interest is positioned within the field-of-view of two fluoroscopes of known
orientation and simultaneous images are taken of the desired joint pose. Next, the
fluoroscopic images are corrected for geometric distortion. Then a virtual dual plane
fluoroscopic imaging system is created in computer space based on the known
orientation of the fluoroscopes during imaging. Three-dimensional models of the
subject’s bones or implants are imported into the virtual environment and matched to
2D features on the acquired image pairs.
From each matched pose, the joint
kinematics has been accurately recreated and the relative position of the bones or
implants can be quantitatively described.
Therefore, this dual plane imaging
matching technique with its non-invasive and accurate nature can be safely applied
to study the kinematics of the shoulder joint complex after total shoulder arthroplasty.
28
2.2 Dual [plane] Fluoroscopic Imaging System (DFIS)
The dual plane fluoroscopic imaging system [DFIS] consists of two standard
mobile C-arm fluoroscopes (12” BV Pulsera, Phillips, USA) arranged with the image
intensifiers slightly skewed from orthogonal to create an imaging volume such that
the human shoulder does not contact either imaging plane during normal motion.
Each C-arm is outfitted with a 12 inch diameter image intensifier such that the
combined imaging volume is approximately 30 x 30 x 30 cm3. This imaging volume
creates a field-of-view that captures the scapula and proximal humerus bones
throughout their normal range of motion such that the system is capable of capturing
the kinematics of the glenohumeral joint during functional daily activities (Fig 8).
Figure 8 Dual plane fluoroscopic imaging system shown with a subject in the central
viewing volume with the shoulder in 90° abduction with maximum external rotation.
29
The distance between the radiation source and the fluoroscopic image intensifier is
approximately 96 cm providing ample room for the subject to freely maneuver within.
The fluoroscopes, in addition to static image capture, have the capability to record
30, 15 and 8 images per second at a uniform distribution. This cinematic image
recording capability allows the DFIS to capture dynamic joint motion in real-time. A
custom switch unit was built to operate both fluoroscopes simultaneously such that
the image pairs recorded are synchronized in time (Fig 9).
Figure 9 Custom switch unit built to operate two fluoroscopes simultaneously with a single input
from the operator. Red and black buttons toggle high and low radiation dosage, respectively.
During each data collection trial, calibration images are taken of radio-opaque ball
bearings (beads) in a known orientation for creation of the virtual DFIS environment
30
and of a copper grid for image distortion correction. The fluoroscopes electronically
record the images with 1024 x 1024 pixel resolution in DICOM file format in 8-bit
grayscale, corresponding to an actual field-of-view that is 295 x 295 mm (Fig 10).
For data analysis, the images are offloaded from the fluoroscopes to a personal
computer and RAID backup storage system.
Figure 10 Typical fluoroscopic image of the shoulder with TSA.
31
2.3 Image Correction & Segmentation
The fluoroscopic images suffer a minimal amount of distortion in the recording
process caused by perturbations of the x-ray beam from the environment and from
the slightly curved surface of the image intensifier.
An adapted polynomial
Gronenschild42, 43 global surface mapping technique is employed to remove the “fisheye” caused by the curved image intensifier surface and “swirl” caused by electromagnetic environmental disturbances. The technique is employed by mapping a set
of polynomial expressions between the actual geometry of a copper grid and the
acquired distorted image of the copper grid (Fig 11).
Figure 11 Typical fluoroscopic image of copper distortion correction plate.
32
Correction of the images is accomplished by using spatial mapping to distort the
image pixels to their “correct” location based on the mapped polynomial expressions
by linearly interpolating the image’s intensity values (Fig 12).
All image pairs
acquired by the DFIS are corrected in this manner before further imaging processing.
300
250
200
150
100
50
0
0
50
100
150
200
250
300
Figure 12 The actual holes in the copper plate are shown as blue diamonds. The distorted
holes as imaged by the fluoroscope are shown as pink triangles. The pink triangles will be
mapped to the blue diamonds using a polynomial expression. (Units in millimeters)
Next, each pair of corrected fluoroscopic images representing a unique shoulder joint
kinematic pose is opened using a custom Matlab (Matlab 7.0.1, The Math Works Inc.,
Natick, MA) script for automated segmentation. The segmentation script is based on
a Canny44 algorithm that uses the gradient of the image’s pixels intensity to
33
determine the outlines of objects in the image.
The script has a graphical user
interface so that the operator can visually check the machine’s performance in
correctly outlining the objects in the image (Fig 13).
In some situations, human
interaction is required to manually modify the machine’s automated segmentation in
areas where the gradient changes slower than the set threshold value. In the case of
total shoulder arthroplasty, the outlines of the glenoid fixation peg beads, humeal
head and stem are saved as points in a text file. The operator discards all other
outlines that were automatically segmented and deemed ancillary.
Figure 13 Typical fluoroscopic image of the shoulder with TSA after being
automatically segmented and manually adjusted for ancillary outlines.
34
2.4 Virtual DFIS Environment & Matching
After fluoroscopic imaging of the subject’s shoulder joint, calibration fixtures
and image distortion correction processing, a replica of the DFIS is created in a
virtual environment. This is accomplished with that data acquired from calibration
images that include the location of the center of the image intensifier and the relative
position of the fluoroscopes. The relative position of the fluoroscopes is determined
by aligning the individual calibration solution of each fluoroscope to one another.
Within solid modeling software (Rhinoceros, Robert McNeel and Associates, Seattle,
WA) the aligned solution is replicated by creating two pairs of virtual sources and
intensifiers such that the replicated geometry is identical to the real fluoroscopic
imaging system (Fig 14).
Figure 14 Virtual DFIS recreated in computer space from the geometry of the actual
fluoroscopic system, shown with CAD models of total shoulder arthroplasty.
35
Next, the pairs of corrected fluoroscopic images and segmented outlines are
imported into the virtual environment and placed on their respective virtual imaging
plane. CAD models acquired from the manufacture that include the glenoid, humeral
head and stem components are introduced into the virtual DFIS.
A coordinate
system is placed at the center of the articular surface of the glenoid component and
the center of humeral head component (Fig 15).
Figure 15 Left scapula shown with glenoid component. Cartesian coordinate
system is created with the origin at the geometric center of the component.
All coordinate systems were defined for the left shoulder joint complex, thus to
simplify data presentation, all right shoulder joints were mirrored to left shoulder
joints. This procedure of importing corrected fluoroscopic images and CAD models is
repeated for each selected pose that was acquired with the real DFIS. In order to
recreate the in-vivo kinematics captured by the DFIS, the imported CAD models must
36
first be matched to the outlines on the virtual fluoroscopic image planes. This is
accomplished by manually co-registering the projected silhouettes of the 3D CAD
models with the 2D outlines of the fluoroscopic images.
The virtual model is
translated and rotated in the virtual DFIS until the 3D model matches the 2D planer
images, at which point the virtual pose recreates the in-vivo pose of the subject
during fluoroscopic imaging.
This matching procedure is repeated for both the
humeral head and stem components.
The in-vivo position of the polyethylene
glenoid component is recreated by orienting three radio-opaque beads inserted in the
fixation pegs to their corresponding bead outlines on the fluoroscopic images. This
matching technique is needed because polyethylene when imaged by a fluoroscopic
imaging device in the presence of high-density radio-opaque material, such as the
cobalt chromium humeral head, tends to ‘wash out’ much of the detail in the image of
the glenoid. Once all poses have been recreated in the virtual environment, analysis
of the coordinates systems placed on the components can be analyzed for relative
motion and contact.
37
2.5 Accuracy & Repeatability
Previously, the accuracy of the DFIS from initial fluoroscopic imaging to
measuring kinematics in the virtual environment was reported using standard
geometries of a sphere and cylinder.
The reported accuracies45 were 0.1mm in
translation and 0.1° in rotation. Similar accuracy is expected in the case of total
shoulder arthroplasty components, where both the humeral head and glenoid fixation
peg radio-opaque marker beads are spherical in geometry.
However, since this
research focuses on the contact location between the humeral head and glenoid
surface, the accuracy of this measure is more relevant than the absolute position and
will be addressed in section 2.6. Thus, an implicit relation of the absolute position is
implied from the accurate measure of the contact location.
To measure the
repeatability of the imaging matching technique a TSA pose was chosen and the
humeral head and glenoid component were independently matched 15 times each.
For each trial the components were randomly oriented in the virtual DFIS, such that
each subsequent match was not affected by the position of the match prior. After all
independent matches were performed; a coordinate system was placed at the center
of the humeral head and glenoid component.
The standard deviation of the
translation and rotation vectors of the coordinate system was taken as the
repeatability of the system to locate each component in space (Table 1).
The
repeatability of the system to match both the glenoid and humeral head components
were approximately the same order of magnitude for the three orthogonal translations
directions and three rotations.
38
Glenoid Component
Mean
Std Dev
x (mm)
-22.53
0.024
Origin
y (mm)
777.22
0.026
x (mm)
-15.76
0.024
Origin
y (mm)
782.06
0.029
z (mm)
-4.62
0.028
x (mm)
-20.66
0.035
Z-Axis
y (mm)
779.08
0.040
z (mm)
5.03
0.030
Normal Vector
I
j
k
1.87
1.86
9.65
0.022
0.027
0.005
Direction Cosines (rad)
alpha
beta
gamma
1.3827
1.3841
0.2666
0.0022
0.0027
0.0019
Humeral Head Component
Mean
Std Dev
z (mm)
11.76
0.016
x (mm)
-17.40
0.035
Z-Axis
y (mm)
782.29
0.036
z (mm)
21.62
0.017
Normal Vector
I
j
k
-1.65
0.24
9.86
0.018
0.012
0.003
Direction Cosines (rad)
alpha
beta
gamma
1.7362
1.5473
0.1671
0.0018
0.0012
0.0018
Table 1 The mean and standard deviations reported for fifteen independent
trials of matching the glenoid and humeral head components.
The system was found to have a minimum repeatability of 0.02mm in translation and
0.07° in rotation and a maximum repeatability of 0.03mm in translation and 0.15° in
rotation. The larger magnitude repeatability in the rotation compared to translation is
attributed the high degree of symmetry that both components share. These results
are on the same order of magnitude as reported for the DFIS system and thus, the
system is capable of measuring the motion of the shoulder after TSA.
39
2.6 Contact & Validation
One objective of this project was to use the DFIS to investigate the contact
locations between the humeral head and glenoid components. The accuracy of the
system was not defined by the actual position of the components, but rather the
ability to accurately determine the centroid of contact.
Therefore, an implicit
relationship holds whereby the ability to accurately measure the contact centroid
implies that a level of accuracy of the system exists such that the positions of the
components in space determine the contact centroid. To verify this relationship and
determine the accuracy of measuring the in-vivo glenohumeral centroid of contact by
the recreated TSA joint position in the virtual environment, a silicon rubber casting
technique was used
46, 47
. First, anatomical total shoulder arthroplasty components
were implanted in a bone substitute and the distal diaphysis of the humerus was
potted in PMMA (Poly [methyl methacrylate] bone cement). The scapula was rigidly
fixed with the normal to the glenoid surface perpendicular to the ground representing
roughly a 90° rotation from the anatomical position to simplify in the load application.
Above the glenoid, the PMMA potted shaft of the humerus was fixed in a cylindrical
jig mounted to a six degree-of-freedom load cell (160M50S; JR3 Inc, Woodland, CA,
USA) attached to the manipulator of an industrial robot (UZ150F; Kawasaki Motors
MFG Corp, Lincoln, NE, USA) (Fig 16). The humerus was positioned to represent
approximately 60° and 90° abduction of the long axis of the humerus in neutral
rotation, taking into account the scapulothoracic rotation with humeral abduction of
approximately two-to-one 28, 48-51.
40
Figure 16 Contact validation setup with robotic manipulation device.
The DFIS was positioned around the glenohumeral joint. The joint was disarticulated
and fast setting silicon rubber (Quick Set; Alumilite CORP; Kalamazoo, MI, USA) was
placed on the glenoid articular surface, immediately followed by application of 350N
from the humeral head in the direction perpendicular to the ground. A force of 350N
was chosen because it was within the range of reported physiologic glenohumeral
loads
24, 38, 52-56
and may approximate the holding of a ten pound weight abducted in
the coronal plane. The silicon rubber set in approximately one minute. Fluoroscopic
images were acquired under load and then the joint was disarticulated. The silicon
rubber was squeezed out of the location where contact occurred between the
humeral and glenoid articular surfaces (Fig 17).
This voided area was digitized
(MicroScribe® G2LX; Immersion CORP; San Jose, CA, USA) along with geometric
landmarks on the glenoid component to facilitate alignment in a virtual environment
41
Figure 17 Silicon rubber impression.
Figure 18 MicroScribe® digitizer.
(Fig 18). Similar to the method presented earlier, a virtual DFIS was created and the
fluoroscopic images corrected for distortion were imported into the virtual
environment. The imaged in-vitro positions of the humerus and glenoid components
were reproduced virtually and the glenoid centroids of contact measured using the
overlap method described in section 3.2 of this document (Fig 19). These manual
pose matching and centroid measurement protocols were repeated twelve
independent times to access the repeatability of the technique. The contact centroid
measured from the overlap method in the virtual environment was compared to the
area centroid measured from the digitized silicon rubber casting taken as the gold
standard (Fig 20). This procedure was repeated for one trial at approximately 60°
42
abduction and two trials at approximately 90° abduction of the long axis of the
humerus in the coronal plane.
Figure 19 The overlap area of the humeral head
and glenoid component is shown in pink. The
black point is the centroid of the pink contact area.
Figure 20 Digitized voided silicon
area on the glenoid component.
The difference in the absolute distance of the measured centroid of contact between
the overlap method and silicon rubber casting technique is listed as Delta X/Y,
respectively in Table 2. To calculate delta, the average contact centroid location from
the twelve independent matches was subtracted from the silicon rubber gold
standard centroid location and the absolute value was taken. In general, for both X &
Y directions, the average offset of the overlap method to the gold standard was at
most 0.30mm, which is on the order of the accuracy of the digitizing equipment. The
repeatability of measuring the contact centroid in the virtual environment was defined
as the standard error of the twelve independent pose match centroid calculations and
listed as SD X/Y Fluoro, respectively in Table 2.
43
On average, for both X & Y
directions, the standard error of repeating the placement of the centroid of contact
with the overlap method on the glenoid surface was approximately 0.1mm. This was
on the order of the accuracy previously reported45 for our method of reproducing invivo joint positions in a virtual environment. Therefore, this non-invasive fluoroscopic
imaging technique can be confidently applied to determine the in-vivo glenohumeral
articular contact locations in patients after TSA.
Trial
90° Abduction (1)
90° Abduction (2)
60° Abduction
Average
Delta X
0.63
0.12
0.15
0.30
Delta Y
0.02
0.03
0.22
0.09
SD X Fluoro
0.04
0.05
0.05
0.05
SD Y Fluoro
0.08
0.10
0.18
0.12
All units in millimeters
Table 2 Delta X and Delta Y, respectively are the difference between the calculated centroid of
contact and the measured centroid using the silicon rubber technique. SD Fluoro X and SD
Fluoro Y, respectively are the repeatability of locating the centroid when independently
matching the glenoid and humeral components within the virtual fluoroscopic imaging system.
44
Chapter 3
3.1 In-Vivo Shoulder Kinematics: Application of Technique
The dual plane fluoroscopic imaging system (DFIS) has been shown to be
both accurate and repeatable in the measurement of the centroid of contact of the
glenohumeral joint. The non-invasive image matching technique, thus easily lends
itself to studying the kinematics of the shoulder joint in the living body. Low radiation
dosage from fluoroscopic imaging is the only risk that the patient encounters during
the study, which has been determined to be low on the benefit-to-risk assessment
performed by the Institutional Review Board (IRB) at the Massachusetts General
Hospital (MGH). A cohort of 13 patients following TSA surgery was recruited for
study under IRB approval.
Each patient was fluoroscopically imaged with the
shoulder joint in various positions representing functional shoulder motion. A virtual
DFIS was recreated for each patient and the kinematics recorded during fluoroscopic
imaging recreated in the virtual environment with CAD models of the joint
components.
Contact centroid analysis was performed and locations recorded
relative to a coordinate system placed at the center of the glenoid component. The
location of the center of the humeral head was measured with respect to the center of
the glenoid component to investigate the coupling of the translation of the humeral
head to the contact measured on the glenoid surface. These data provide a basis
which to compare other surgeons’ results and compare against normal contact
locations in healthy individuals. The measurements may help to improve implant
designs and surgical implantation technique; and ultimately to enhance component
longevity and increase patients’ ROM and functionality after TSA.
45
3.2 Total Shoulder Arthroplasty - Study Design
A total of 13 patients who underwent anatomic TSA (Anatomical Shoulder;
Zimmer, Warsaw, IN, USA) from 1999-2005 were recruited from the practice of the
same orthopaedic surgeon.
This study was approved by the institutional review
board at our institution and informed consent was obtained from all patients before
participating. There were eight men and five women with an average age of 61 years
(range: 37-72 years) at the time of surgery. All patients had clinically successful
outcomes and were imaged for this biomechanics study at least 12 months (average:
32 months, range: 12-88 months) after the date of implantation. At the time of study,
all patients were without pain and had a complete range of shoulder motion. One
man had bilateral total shoulders. In total there were nine left shoulders and five right
shoulders imaged (14 total). One female patient with a right TSA was not able to be
analyzed due to motion artifact captured during the image acquisition process. The
remaining eight men and four women with nine left and four right TSA (13 total) were
investigated in this study.
Shoulder contact kinematics were measured using a dual plane fluoroscopic
imaging system (DFIS) as described in section 2.2. The fluoroscopes (BV Pulsera;
Philips, Bothell, WA, USA) were positioned around the shoulder of interest and
allowed the patient to sit comfortably on a stool while providing ample clearance to
freely move their arm without bumping the imaging system (Fig 8). A gonimeter was
used to control the abduction angle (in the coronal plane) of the humerus with
46
respect to the sagittal plane of the body. The patient was protected from radiation
exposure by custom lead aprons from the thyroid to just above the knee joint. Mirror
image right and left lead vests were manufactured with lead deletes around the
respective shoulder complex that allowed unobstructed fluoroscopic imaging of the
joint while providing radiation protection to nearby vital organs.
Each patient
underwent no more than eight pairs (16 total fluoroscopic images) of simultaneous
fluoroscopic images, each patient receiving a maximum of 6 mrem of ionizing
radiation.
The shoulder of interest was first imaged at 0° abduction of the humerus in
neutral rotation (humerus perpendicular to the ground, elbow in full extension, palm
parallel to the sagittal plane) in the coronal plane while the patient sat relaxed on a
stool. The patient then lifted their arm to 45° of abduction of the humerus in neutral
rotation (no axial rotation of the forearm with respect to the longitudinal axis of the
humerus, elbow in full extension) and was simultaneously imaged by both
fluoroscopes. Similarly, the shoulder was imaged with the humerus in 90° abduction
neutral rotation (elbow in full extension, palm parallel to the ground).
Next the
shoulder was imaged, with the humerus in 90° abduction; the patient flexed the
elbow to 90° of flexion (palm parallel to the ground) and then actively rotated the
shoulder into maximum external rotation. This position was similar the cocked phase
of throwing motion and is the position that the shoulder is at risk for anterior
instability. Finally, the shoulder was actively rotated about the longitudinal axis of the
humerus in 90° abduction (elbow in 90° flexion) to maximum internal rotation, to
47
represent the opposite position to the cocked phase of throwing motion and
simultaneous fluoroscopic images were acquired.
These positions were chosen
because they simulate the shoulder motion required for functional living activities
such as combing one’s hair.
All trials were conducted under the weight of the
patient’s own forearm. No additional weight was held by the subject.
Using the DFIS technique described in this thesis, the geometry of the dual
plane fluoroscopic imaging system was recreated in solid modeling software
(Rhinoceros 4.0; McNeel, Seattle, WA, USA) to create a virtual dual plane
fluoroscopic imaging system. All acquired image pairs were corrected for geometric
distortion. Each patient’s images were placed on their respective virtual fluoroscopic
intensifier and three-dimensional CAD models of the patient’s humeral head and
glenoid components were introduced into the virtual environment. The position of the
humeral head was manually manipulated in the virtual environment until its
projections matched the outlines on the fluoroscopic images in both planes. The invivo position of the polyethylene glenoid component was reproduced in the virtual
environment by aligning the projections from the acquired images of the radioopaque beads implanted by the manufacturer as part of standard production in the
three outermost pegs to the beads that are part of the CAD glenoid model. This
procedure of recreating the in-vivo glenohumeral joint positions with CAD models in a
virtual environment was repeated for all patients’ image pairs acquired.
The
accuracy of this method to determine the six degree-of-freedom in-vivo joint positions
in a virtual environment has been reported in our previous work45, where the method
48
was shown to have a translational accuracy of 0.1mm and rotational accuracy 0.1° in
three-dimensions.
For each recreated in-vivo glenohumeral joint position in the virtual
environment, the relative motion of the humeral head to the center of the glenoid
component and the centroid of articular surface contact between the CAD models of
the humeral head and glenoid were determined.
To determine the centroid of
contact, the overlap area of the articular surfaces of the humeral head and glenoid
was defined on the glenoid component articular surface and the geometric area
centroid calculated. In the event that overlap between the articular surfaces was not
detected, the point of minimum normal distance from the glenoid articular surface to
the humeral head was defined as the contact location. This method was verified with
a silicon rubber casting technique46,
47
; details are presented in section 2.6.
To
quantify the humeral head motion and the contact location on the glenoid surface, a
Cartesian coordinate system was placed at the geometric center of the glenoid
articular surface and the humeral head component. For the glenoid, the superiorinferior axis was defined as the Y-axis and is approximately collinear with the medial
scapular spine.
The anterior-posterior axis was defined as the X-axis and is
perpendicular to the Y-axis, shown in Figure 15. The distance ( X 2 + Y 2 ) from the
glenohumeral contact centroid to the origin of the Cartesian coordinate system was
measured for all patients in all imaged shoulder positions.
To quantify the
glenohumeral contact patterns of the patients, contact centroid locations were
discretized into a quadrant occupancy percentage, defined as the discrete number of
49
contact occurrences within a quadrant to the total number of positions examined.
Data presentation was made consistent by mirroring all right glenoid contact locations
to left glenoid contact locations. Contact centroid locations are presented unscaled
on the implanted size of the patient’s glenoid component (small, medium or large).
50
3.3 Glenohumeral Contact Results
Patient specific TSA glenohumeral joint contacts on the glenoid component
surface are shown in Figure 21. The observed contact patterns were varied among
the patients as visualized by the colored coded locations. The raw data for the
contact locations on the glenoid surface are shown in Table 3.
Figure 21 Unscaled patient specific contact locations on the glenoid surface as a function of arm position,
shown by color code. All right shoulder contact locations were mirrored to left glenoid components.
0° to 45° abduction neutral rotation
All patients showed superior translation of the contact centroids; the average
superior translation was 13.6mm. Six of 13 patients had posterior translations; the
average posterior translation was 4.6mm.
Seven patients showed anterior
translations on the glenoid articular surface; the average anterior translation on the
glenoid surface was 4.0mm.
51
45° to 90° abduction neutral rotation
Seven of 13 patients had superior translations; the average superior
translation was 5.3mm. Six patients showed inferior translations; the average inferior
translation was 2.9mm. Six of 13 patients had posterior translations; the average
posterior translation was 1.6mm. Seven patients showed anterior translations on the
glenoid surface; the average anterior translation was 2.7mm
90° abduction neutral rotation to maximum external rotation
Four of 13 patients showed superior translations; the average superior
translation was 3.0mm. Nine patients had inferior translations on the glenoid articular
surface; the average inferior translation was 5.4mm. Seven of 13 patients showed
posterior translations; the average posterior translation was 3.0mm. Six patients had
anterior translations; the average anterior translation was 3.9mm.
90° abduction maximum external rotation to maximum internal rotation
Eight of 13 patients had superior translations; the average superior translation
was 8.4mm. Five patients showed inferior translations on the glenoid surface; the
average inferior translation was 4.9mm.
Five of 13 patients had posterior
translations; the average posterior translation was 6.8mm. Eight patients showed
anterior translations; the average anterior translation was 6.3mm.
52
0°
45°
90°
Max 90ER
X
Y
Max 90IR
X
Y
X
Y
X
Y
X
Y
1
Left
2.9
4.3
1.3
9.4
0.2
10.3
4.7
15.2
0.1
11.1
3
Left
8.9
5.3
4.9
13.2
5.7
16.7
-2.5
7.4
10.5
-4.5
4
Left
-13.5
-10.3
-8.1
4.7
-4.9
1.3
-3.2
6.3
5.9
2.1
5
Right
9.2
-6.3
9.4
9.9
9.1
10.6
8.3
12.2
0.9
16.8
6
Right
-0.5
-2.1
-2.4
5.7
-7.8
8.2
-2.4
8.0
2.3
6.1
7
Left
4.1
-17.6
-7.1
9.3
-5.2
7.9
0.5
3.5
-9.0
4.1
8
Left
2.6
-11.9
4.5
4.5
2.8
2.4
0.9
2.1
0.9
11.6
9
Right
5.9
9.4
4.3
13.9
5.1
10.7
6.8
5.2
0.9
14.9
9
Left
14.3
-4.2
9.6
11.3
10.6
4.7
11.6
-0.4
0.5
17.1
10
Left
13.9
-8.9
14.3
-6.8
6.3
13.5
3.7
11.5
-1.8
14.9
11
Left
-5.8
-18.6
6.1
9.4
8.1
8.9
-1.3
-2.7
2.8
14.8
12
Left
-3.7
-12.3
4.3
4.1
2.9
13.0
3.9
2.5
7.1
0.2
13
Right
11.6
-10.5
8.6
3.9
7.6
All units in millimeters
4.2
7.6
4.5
0.7
8.6
Patient Shoulder
Table 3 The locations of the glenohumeral contact on the glenoid surface. The data is
not scaled for component size. Data presentation is made consistent by mirroring all
right shoulders to left glenoid components.
In all 65 positions examined, no contact was found at the geometric center (origin) of
the glenoid component (Table 4). In all positions, the centroid of articular contact
was on average 11.0 ± 4.3mm away from the center of the component. Contact
locations in 0° abduction of the humerus in neutral rotation were on average the
furthest away from the center of the glenoid at 12.8 ± 5.0mm. The contact centroids
in 90° abduction of the humerus in the coronal plane with maximum active external
rotation were on average the closest to the glenoid center at 8.3 ± 4.4mm.
53
Shoulder
1
2
3
4
5
6
7
8
9
10
11
12
13
Average
Std Dev
Min
2.2
0°
5.2
10.4
17.0
11.2
2.2
18.1
12.2
11.1
14.9
16.5
19.4
12.8
15.6
12.8
5.0
45°
9.5
14.1
9.4
13.6
6.2
11.7
6.4
14.6
14.8
15.8
11.2
6.0
9.5
11.0
3.5
6.0
90°
10.3
17.7
5.1
14.0
11.3
9.5
3.7
11.9
11.6
14.9
12.1
13.3
8.7
11.1
3.8
3.7
Max 90ER 15.9
7.8
7.1
14.7
8.4
3.6
2.3
8.6
11.6
12.1
3.0
4.6
8.8
8.3
4.4
2.3
Max 90IR
11.4
6.3
16.8
6.5
9.9
11.6
14.9
17.1
15.0
15.1
7.1
8.6
11.6
3.9
6.3
11.1
All units in millimeters
Table 4 Radial distance of the contact centroid from the center of the glenoid
component. Data is not scaled for glenoid component size.
Glenohumeral joint contact was predominantly on the superior-posterior quadrant
(Q1) of the glenoid surface representing 61.5% of the total contact for all positions
(Fig 22). 21.5% (14 of 65) of the total contact was inferior to the glenoid horizontal
midline, 10 of these 14 contacts were at 0° abduction neutral rotation. Quadrant
three, the inferior-anterior quadrant saw only 7.7% (5 of 65) of the total contact,
where four of these five contacts were at 0° abduction neutral rotation. The other (1
of 5) contact in quadrant three was at 90° abduction with maximum active external
rotation (Fig 23).
In 45° abduction, only one patient had contact in the inferior-
posterior (Q4) quadrant, this same patient had contact in Q4 at 0° abduction, the
distance between the contact centroids was 2.08mm.
In general, the contact
frequency distributions were similar for all shoulder positions except 0° abduction of
the humerus in the coronal plane with neutral rotation. If we ignore this position,
92.3% (48 of 52) of the glenoid contact was superior to the horizontal midline with
active abduction of the humerus.
54
70
61.5
Percent Occupancy (%)
60
50
40
30
20
16.9
13.8
7.7
10
0
Q1
Q2
Q3
Q4
Discrete Quadrant Location
Figure 22 Percent occupancy per quadrant to all shoulder positions imaged.
12
Q1
Q2
Q3
Q4
Discrete Frequency
10
8
6
4
2
0
0°
45°
90°
90° Max ER
90° Max IR
Humerus Position WRT Vertical
Figure 23 Discrete frequency of quadrant contact per shoulder position imaged.
55
3.4 Humeral Head Kinematics Results
Patient specific humeral head center locations on the glenoid component
surface are shown in Figure 24. The observed humeral head center locations were
varied among the patients as visualized by the colored coded locations. The raw
data for the contact locations on the glenoid surface are shown in Table 5.
Figure 24 Unscaled patient humeral head center locations on the glenoid surface as
a function of arm position, shown by color code. All right shoulder humeral head
centers locations were mirrored to left glenoid components.
0° to 45° abduction neutral rotation
All patients showed superior translation of the humeral head center relative to
the center of the glenoid; the average superior translation was 3.5mm. Ten of 13
patients had posterior translations; the average posterior translation was 1.4mm.
Three patients showed anterior translations of the humeral head center; the average
anterior translation was 1.6mm.
56
45° to 90° abduction neutral rotation
Four of 13 patients had superior translations of the humeral head center; the
average superior translation relative to the center of the glenoid was 1.9mm. Nine
patients showed inferior translations; the average inferior translation was 1.0mm.
Five of 13 patients had posterior translations; the average posterior translation was
1.6mm. Eight patients showed anterior translations of the humeral head center; the
average anterior translation was 1.1mm
90° abduction neutral rotation to maximum external rotation
Three of 13 patients showed superior translations; the average superior
translation was 0.3mm. Nine patients had inferior translations of the humeral head
center relative to the glenoid; the average inferior translation was 1.2mm.
One
patient did not translate superior-inferior during this shoulder position. Seven of 13
patients showed posterior translations; the average posterior translation was 1.1mm.
Six patients had anterior translations; the average anterior translation was 0.9mm.
90° abduction maximum external rotation to maximum internal rotation
Nine of 13 patients had superior translations; the average superior translation
was 2.2mm. Four patients showed inferior translations of the humeral head center
relative to the glenoid; the average inferior translation was 0.6mm.
Five of 13
patients had posterior translations; the average posterior translation was 2.0mm.
Eight patients showed anterior translations; the average anterior translation relative
to the center of the glenoid was 2.7mm.
57
0°
Patient Shoulder
45°
90°
X
Y
X
Y
X
Y
Max 90ER
X
Y
Max 90IR
X
Y
1
Left
0.3
0.5
1.4
4.1
0.1
2.1
1.2
2.3
0.0
2.4
3
Left
2.0
0.9
2.2
3.5
0.7
2.0
-0.3
1.0
3.2
-0.6
4
Left
-3.4
-1.8
-2.5
0.9
-0.7
0.2
-0.5
0.9
2.0
0.5
5
Right
1.0
-0.6
2.7
1.3
3.4
1.7
2.1
1.0
0.1
1.6
6
Right
-1.3
-1.0
-0.3
0.7
-1.0
1.1
-0.3
1.1
0.3
0.9
7
Left
1.3
-4.9
-1.6
2.1
-1.2
1.8
0.1
0.8
-2.1
0.9
8
Left
1.1
-3.4
1.6
1.0
1.0
0.5
3.0
0.6
0.4
3.0
9
Right
1.3
1.4
2.6
4.5
2.2
2.5
3.4
1.4
0.6
5.2
9
Left
2.7
-0.8
1.9
2.2
6.7
1.8
7.7
0.2
0.2
4.4
10
Left
2.7
-1.5
3.5
-1.1
1.5
2.6
0.6
1.9
-0.7
4.2
11
Left
-2.5
-6.0
2.6
2.4
1.1
1.2
-0.2
-0.3
1.4
4.7
12
Left
-0.6
-1.8
1.2
0.7
1.6
3.9
0.9
0.4
2.8
0.1
13
Right
5.0
-2.6
3.8
1.1
2.8
All units in millimeters
1.0
2.6
1.0
0.4
2.1
Table 5 The locations of the humeral head center on the glenoid surface. The
data is not scaled for component size. Data presentation is made consistent by
mirroring all right shoulders to left glenoid components.
In all 65 positions examined, the humeral head center was not centered at the
geometric center (origin) of the glenoid component (Table 6). In all positions, the
center of the humeral head was on average 2.8 ± 1.6mm away from the center of the
glenoid component. Humeral head centers in 0° abduction of the humerus in neutral
rotation were on average the furthest away from the center of the glenoid at 3.1 ±
1.8mm. The contact centroids in 90° abduction of the humerus in the coronal plane
with maximum active external rotation were on average the closest to the glenoid
center at 2.3 ± 1.9mm.
58
Shoulder
1
2
3
4
5
6
7
8
9
10
11
12
13
Average
Std Dev
Min
0°
0.6
2.2
3.8
1.2
1.6
5.0
3.5
2.0
2.8
3.1
6.5
1.9
5.6
3.1
1.8
0.6
45°
4.3
4.2
2.7
3.0
0.8
2.6
1.9
5.2
2.9
3.6
3.5
1.4
4.0
3.1
1.3
0.8
90°
2.1
2.1
0.8
3.8
1.5
2.1
1.1
3.3
6.9
3.0
1.7
4.2
3.0
2.7
1.6
0.8
Max 90ER
2.6
1.1
1.0
2.4
1.1
0.8
3.1
3.7
7.7
2.0
0.4
1.0
2.8
2.3
1.9
0.4
Max 90IR
2.4
3.2
2.1
1.6
0.9
2.3
3.0
5.2
4.4
4.3
4.9
2.8
2.1
3.0
1.3
0.9
All units in millimeters
Table 6 Radial distance of the center of the humeral head from the center of the
glenoid component. Data is not scaled for glenoid component size.
The humeral head center was predominantly on the superior-posterior quadrant (Q1)
of the glenoid surface representing 63.1% of the total contact for all positions. 20.0%
(13 of 65) of the total contact was inferior to the glenoid horizontal midline, 10 of
these 14 contacts were at 0° abduction neutral rotation. Quadrant three, the inferioranterior quadrant saw only 7.7% (5 of 65) of the total contact, where four of these five
contacts were at 0° abduction neutral rotation. The other (1 of 5) contact in quadrant
three was at 90° abduction with maximum active external rotation. In general, the
contact frequency distributions were similar for all shoulder positions except 0°
abduction of the humerus in the coronal plane with neutral rotation. If we ignore this
position, 94.2% (49 of 52) of the glenoid contact was superior to the horizontal
midline with active abduction of the humerus.
59
3.5 Coupled Motion
Patient specific glenohumeral contact locations on the glenoid and humeral
head center locations on the glenoid component surface are shown in Figure 25.
The glenoid contact locations translated on the glenoid surface in the same direction
as the humeral head center, but at a smaller magnitude as visualized by the colored
coded locations. The raw data for the contact locations and humeral head centers on
the glenoid surface are shown in Table 3 and Table 5, respectively.
Figure 25 Unscaled patient specific glenoid contact locations and humeral head center
locations on the glenoid articular surface as a function of arm position, shown by color code.
All right shoulder locations were mirrored to left glenoid components.
The direction of the glenohumeral contact centroid followed the direction of the
humeral head center (Fig 25).
The glenohumeral contact translation in the X
direction was on average 2.6 times greater than the translation of the humeral head
center. Similarly, the glenohumeral contact translation in the Y direction was on
60
average of 4.0 times greater than the translation of the humeral head center (Fig 26).
Both X and Y slope linear regressions were found significant at p<0.001.
Glenoid Contact Centroid Translation (mm)
20
X-Axis
15
Y-Axis
10
5
0
-6
-4
-2
0
2
4
6
8
-5
Xg = 2.6Xh
R2 = 0.74
-10
Yg = 4.0Yh
R2 = 0.84
-15
-20
-25
Humeral Head Center Translation (mm)
Figure 26 Plot of the glenoid contact centroid translation versus the humeral head center translation,
showing the ratio of glenohumeral contact translation to the humeral head in X and Y directions.
The ratio of the X coupling to the Y coupling of the glenoid contact location to the
center of the humeral head is given by:
2.6
= 0.65
4.0
The ratio of the average physical dimensions of the glenoid cavity is10:
23mm + 29mm
= 0.67
2 (39mm )
The amount of measured translation in patients after TSA of the glenoid contact
location to the humeral head center is approximately proportional to the physical
dimensions of the glenoid component as shown by comparing the ratios 0.65 ~ 0.67.
61
3.6 Discussion - Comparison With Previous Results
A restored range of motion, pain relief1 and durability are primary outcomes
sought by patients after TSA for treatment of end-stage shoulder degeneration. The
prosthetic shoulder implant design and surgical technique together help facilitate
these patient goals. However, component failures, such as glenoid loosening and
polyethylene damage have been reported in the literature3-7. To this end, in-vivo
glenohumeral joint contact kinematics are necessary for the improvement of implant
design and surgical implantation technique; and ultimately to enhance component
longevity. Therefore, the purpose of this study was to quantify the glenohumeral
kinematics in patients after anatomic TSA and report their humeral head center
translations and glenoid contact locations using a non-invasive dual plane
fluoroscopic imaging technique. In doing so, we proved our null hypothesis that
anatomic TSA glenohumeral articular joint contact is not centered on the glenoid
surface. Furthermore, there was contact variation among the patients and contact
centroids translated significantly on the glenoid surface demonstrating that contact
kinematics are not ‘ball-in-socket’ as traditionally thought17, 24, 26-28.
Several cadaveric studies have documented the healthy glenohumeral
articular contact locations in-vitro, however no study has reported on TSA contact
kinematics.
For example, Conzen and Eckstein57 in cadavera without shoulder
pathology used FUJI Prescale film to show that only parts of the glenoid fossa exhibit
contact under load, they reported both central and bicentric (superior-inferior) contact
62
areas. Specifically, during normal abduction in the scapular plane without external
rotation, they found 3 of 10 glenohumeral joints with central contact, 4 of 10 with
bicentric (superior-inferior) contact and 3 of 10 with mixed contact areas.
They
reported that with increasing abduction of the humerus there was a superior
migration of the contact area in the specimens with central contact patterns (3 of 10).
Additionally, they reported that superior migration was found in the joints of bicentric
(superior-inferior) load-bearing areas (4 of 10), but that this was less obvious than
with the central contact area specimens. Likewise, Soslowsky et al. found with a
sterophotogrammetry analysis58 that at 0° abduction in the humeral starting rotation,
contact on the glenoid was split 74% anterior and 26% posterior. They found that as
the humerus increased abduction, the contact area shifted slightly posterior. Thus, at
60° abduction, the contact was 63% anterior and 37% posterior, and at 120°
abduction, the contact was 62% anterior and 38% posterior, and finally at 180°
abduction, the contact was 37% anterior and 63% posterior. Additionally, Soslowsky
et al. described a slight inferior shift of contact on the glenoid fossa with increasing
abduction of the humerus from 0° to 180° abduction.
The results of Conzen and Eckstein57 are contrasted with our present study
where we report that the majority of contact is in the superior-posterior quadrant of
the glenoid component, as opposed to central or superior-inferior contact. Also, we
did not observe any bicentric or multi-point contact on the glenoid surface, which may
be explained by the rigid materials of shoulder prosthetics compared to natural
compliant articular cartilage.
Soslowsky et al. report58 that at 0° abduction,
63
approximately 38% of the contact was on the inferior glenoid surface, however we
found 77% (10 of 13) of contact on the inferior glenoid surface. Additionally at 0°
abduction, Soslowsky et al. report approximately 51% of the contact in the superioranterior quadrant of the glenoid surface; in contrast we found no contact in this
shoulder position and quadrant.
However, the results presented in this thesis do parallel a previous study
conducted in our lab59 where we reported that the in-vivo glenohumeral joint contact
centroids of healthy volunteers are not centered and translated significantly on the
glenoid surface. We also found similar contact frequencies for the inferior-anterior
quadrant, having reported a 4% (1 of 25) contact frequency in the normal subjects
and a 7.7% (5 of 65) contact frequency in anatomic TSA patients. These results
suggest that anatomic TSA shoulder mechanics do not follow ‘ball-in-socket’ motion
and result from the recreated anatomic glenohumeral geometry.
The recreated
glenohumeral anatomy in TSA patients is accomplished through the correct sizing of
the humeral and glenoid components coupled with surgical implantation in an
anatomic orientation.
Anatomically designed shoulder components incorporate a
radial mismatch4, 5, 13, 25, 60 between the radius of curvature of the humeral head and
glenoid articular surface to mimic the radial mismatch between the articular cartilage
surfaces of the native joint10-12, 17. This radial mismatch in anatomic TSA allows the
implanted humeral head component to translate on the glenoid surface just as found
in the healthy volunteer shoulders, thereby recreating a normal motion pattern that is
not ‘ball-in-socket.’
64
The observed contact patterns in this study, specifically the preferred contact
in the superior-posterior quadrant of the glenoid surface representing 40 of 65 total
positions imaged is not explained from the anatomic geometry alone. Because the
geometric symmetry of the components should not favor any one quadrant on the
glenoid surface, when the concave, convex and compressive nature of the
glenohumeral joint should favor centered contact, which our study has shown
otherwise.
In support of this preferred contact, retrieval studies have found
significant damage in the superior-posterior portion of retrieved glenoid components6,
7
. The reason for preferred superior-posterior contact in TSA patients is currently
unknown; although several factors could be soft tissue balance of the rotator cuff,
glenoid version and priopreceptive neuromuscular control.
Nevertheless, 0°
abduction of the humerus with neutral rotation in the coronal plane exhibited the
greatest variation of contact quadrant frequency, yet no contact was found on the
superior-anterior quadrant. In general, the contact centroids at 0° abduction were the
most inferior of all positions imaged and may result from a lack of isometric muscle
contraction (relaxed muscles) needed to maintain this arm position compared to the
other arm positions studied, thus allowing the humeral head to translate inferiorly on
the glenoid surface. To delineate this inferior contact phenomenon, future studies
should ask the patient to shrug their shoulder in this position, both with and without
additional weight held in the hand.
Previous studies have investigated the motion of the center of the humeral
head relative to the glenoid center.
Poppen and Walker28 used plane film two
65
dimensional x-rays to investigate the in-vivo superior-inferior motion, reporting that
the average translation was 1.09 ± 0.47mm. Harryman et al. investigated the three
dimensional translation of the humeral head center using a magnetic tracking system
in cadavers23. Using an MRI technique Rhoad et al. reported the in-vivo motion in
the anterior-posterior direction as ±2.1mm and the superior-inferior direction ±1.7mm
away from the center of the glenoid61. Similarly Schiffern et al. using an MRI testing
protocol measured the in-vivo anterior-posterior translation as 1.9mm in the anterior
direction and 2.2mm in the posterior direction62. The various reported values for the
translation of the humeral head center can possibly be attributed to the measuring
techniques. For MRI measurements, the patient is lying supine and the shoulder is
held in the position of interest for several minutes for each pose image. By having
the patient lie supine, the direction of gravity is changed from acting in the superiorinferior direction to the anterior-posterior and may affect the amount of measured
translation. In addition, the shoulder is supported in the MR machine for each pose
and may allow the muscles of the rotator cuff to relax causing the measured
translations to be greater than they would be under dynamic conditions.
Comparing the measured humeral head translations after TSA found in this
study to that of previous studies is challenging because the motions of the shoulder
were different for each study. However, for all positions examined (65 total) the
average anterior-posterior location and average translation was 1.2mm ± 2.0mm and
the average superior-inferior location and average translation was 1.0mm ± 2.1mm.
Thus on average the location of the center of the humeral head was 1.2mm posterior
66
and 1.0mm superior, which is consistent with having 63.1% of the humeral head
center locations in the superior-posterior quadrant. The average translations are
similar to those previously reported61, 62 and may suggest that the amount of humeral
head translations are relatively insensitive to measurement technique and shoulder
position.
The data suggests the center of the humeral head remains relatively
centered on the origin of the glenoid component within approximately ±2mm in both
the X and Y direction. However, this small translation is not ‘ball-in-socket’ which
implies that the contact centroid of the glenoid and humeral head remain centered on
the glenoid component. This coupling of the translation of the humeral head and the
glenoid contact location was shown in Figure 25, where the location of the humeral
head center directly effected the location of the contact. Such that, the observed
strong translational coupling between the humeral head center and glenohumeral
articular contact centroid shows that for small translations of the humeral head center
the glenoid contact can shift significantly on the glenoid articular surface; thus
indicating the effect of glenohumeral radial mismatch4,
5, 13, 25, 60
on shoulder joint
contact biomechanics.
The effect of radial mismatch was investigated, although the low sample size
of 13 shoulders was not significant to find how the radial mismatch may influence the
translation of the humeral head on the glenoid surface after TSA. Walsh et al. has
said that the ideal radial mismatch is between 5mm and 7.5mm, although these
values were determined primarily from minimizing the radiolucency of the glenoid
component in the scapula bone and not from understanding the translations of the
67
humeral head and the effect on the glenohumeral contact location4,
63
.
A radial
mismatch of 2.7mm to 7.4mm was recorded for the 13 patients investigated in this
study. There was not a relationship between the radial mismatch and the observed
translation of the humeral head. Future studies should include a large sample of
patients with a wide range of radial mismatches to discern how the mismatch amount
may affect the magnitude of the humeral head center and the amount of influence
that the translation of the humeral head has on the contact centroid of the
glenohumeral joint. These results may have significant implications for component
designs and the ultimate longevity of the components.
68
Chapter 4
4.1 Discourse
This work quantified for the first time the in-vivo glenohumeral joint contact
locations and humeral head centers in patients after TSA using a non-invasive threedimensional image matching technique. The glenohumeral contact locations and
humeral head translations are unique to the 3D ability of the technique presented in
this thesis. Previous studies have sought to quantify the humeral head translations
relative to the glenoid in both normal and TSA patients, however, the limitations of
the previous methods23, 28, 61, 62 may reduce the clinical and biomechanical impact of
the results.
assessments.
The previous methods can be broken down to in-vitro and in-vivo
In-vitro measurements have the advantage of using invasive
measurement techniques, but suffer from the lack of dynamic physiological muscle
loading.
The absence of muscle loading significantly alters the humeral head
translations and thus effects the glenohumeral contact locations.
Current in-vivo
techniques for measuring humeral head translations, however sophisticated, suffer
from limited accuracy and 3D analysis. Thus the techniques presented in this work
address the short comings of previous in-vitro and in-vivo analysis of shoulder joint
kinematics. The method presented provides a structured approach for measuring the
in-vivo shoulder kinematics under physiological loading conditions to analyze
humeral head translations and glenohumeral joint contact locations.
69
4.2 Advantages & Limitations
Although this thesis seeks to address the limitations of previous research, the
study design is not without its own set of limitations. Our patient population was
limited to 13 clinically successful TSA operations and their resultant contact
kinematics without distinguishing gender and dominance differences. The relative
implanted position of the glenoid component to the glenoid vault orientation with
respect to preoperative x-ray or CT image studies and its effect on glenohumeral
contact locations was not assessed.
Thus, the amount of glenoid version and
superior-inferior tilt corrected for in the reaming process of the TSA procedure could
not be correlated to posterior contact on the glenoid articular surface. In addition, all
shoulder orientations examined in this study were imaged under static conditions by
the dual plane fluoroscopic imaging system. However, the patient was required to
dynamically stabilize and position their arm to the desired shoulder orientation of
interest and actively hold this pose for approximately five seconds for image
alignment and acquisition. Glenohumeral joint loading was under forearm weight
only; no additional weight was held by the patients during abduction and internal and
external rotation motions. Future studies should quantify gender and dominance
differences, the effect of glenoid version on contact centroids, dynamic glenohumeral
joint contact motion and the effect that increased glenohumeral loading has on
contact locations.
70
Another limitation of this study revolves around the overlap method for
determining the contact centroid between the glenoid and humeral head component.
Specifically the dimensional differences between the components CAD models and
the machined parts tolerances that coupled with the positional accuracy of the
components placement in the virtual environment affect the amount of component
overlap and thus the location of the contact centroid. However, rigorous validation of
this method is presented in section 2.6 and shows that in spite of these technical
challenges, the overall system’s ability to measure the contact centroid location is
highly repeatable and accurate.
This overlap method was applied to 48 of 65
positions in the virtual environment, 17 other shoulder positions did not show overlap
between the glenoid and humeral head components.
In these 17 cases, the
minimum normal distance between the components articular surfaces were found
and defined as the contact centroids. For these reasons, it is important to remember
that this thesis presents the centroids of contact and not that of actual contact areas
of the glenohumeral joint following TSA. Nonetheless, the data from this study may
provide an insight to shoulder biomechanics and help with understanding damage
mechanisms of the polyethylene glenoid component in-vivo.
71
4.3 Future Work
The data and validated technique from this thesis provide the insight
necessary to investigate other shoulder joint related kinematics questions. The noninvasive image matching technique was modified to use cinematic fluoroscopic image
acquisition in place of static image capture as recorded in the glenohumeral contact
locations presented in this work.
Cinematic image capture allows the real-time
dynamic motion capture of the shoulder joint at 30, 15 and 8 images per second at a
uniform distribution.
This method was applied to investigate the dynamic
scapulothoracic kinematics in a patient after TSA. The results are the first to suggest
that the relative contribution of the glenohumeral and scapulothoracic joints on
abduction and adduction may not be constant as previously thought. Similarly, the
DFIS was validated using a cadaver model to assess the systems ability to
accurately track bone models compared to the bead tracking method taken as the
‘gold standard’ during dynamic motion of the shoulder joint complex.
The
assessment has shown that the DFIS is accurately able to measure the kinematics of
the native joint non-invasively and opens the door to investigate real life problems
such as understanding the kinematics of throwing a baseball or lifting a weight. In
addition, these data provided a validated and accurate technique that can be used to
apply for grant funding and investigate larger populations to establish a database of
‘normal’ shoulder motion which can be used as the comparison for future studies of
pathologic shoulder conditions to investigate the effect that surgical modalities and
treatment efficacies have on the restoring shoulder joint motion.
72
4.3.1 Dynamic Scapulothoracic Kinematics After TSA
Introduction
Preserving scapular function following total shoulder arthroplasty (TSA) is
essential for maintaining the normal range of dynamic motion of the shoulder joint
complex.
However, the ability to accurately measure in-vivo glenohumeral and
scapular motion remains a challenge in the field of bioengineering. Single plane
radiography was used to explore scapular rotation, but is limited to motion parallel to
the imaging plane50. Bi-plane x-ray systems have been developed to overcome this
limitation; however, these systems can suffer from relatively high radiation dosages41,
64
. To minimize these effects, 6DOF electromagnetic tracking devices have been
attached to the shoulder joint complex to measure scapulothoracic kinematics;
except at large humeral abduction angles they can suffer skin motion artifacts65,
66
.
The purpose of this study was to investigate the feasibility and repeatability of using
dual orthogonal cine fluoroscopy to quantify the dynamic scapular motions of living
subjects after anatomic TSA.
Material and Methods
One TSA patient with anatomical shoulder components (Anatomical Shoulder
System, Zimmer, Warsaw, IN) was recruited under IRB guidelines and informed
consent. The replaced shoulder was scanned at 30 frames per second while the
patient performed dynamic abduction and adduction in the field of view of two
fluoroscopes (BV Pulsera, Philips, Bothell, WA). The shoulder was scanned in a
cycle from approximately 27° to 55° abduction/adduction over a period of six
73
seconds. The fluoroscopic images and CAD models were used to create a virtual
dual fluoroscopic imaging system (DFIS)45. The scapular motions were tracked by
matching the glenoid model using radiographic beads implanted in the glenoid
fixation pegs from the manufacture to the fluoroscopic images. Similarly, the humeral
components were tracked by matching the outlines of their CAD models to the
fluoroscopic images. The in-vivo scapular position at each abducted/adducted and
rotated position was therefore reproduced using the TSA models.
From these
models, a coordinate system was placed at the center of the glenoid articular surface
and tracked through selected frames of the imaging sequence (Fig 27). The first
frame of the sequence served as a normalization for geometric comparison of the
scapular motions during the imaging period (Fig 28). The repeatability of reproducing
the scapular motion was evaluated by comparing the scapular motion determined by
six independent glenoid matches of selected position within the motion cycle.
Results
In-vivo scapular rotation kinematics in 6 DOF after anatomic TSA have been
reported relative to a normalized coordinate reference system during a 30°
abduction/adduction cycle of the humerus relative to the vertical. Figure 29 shows
the rotations about the axes created at the center of the glenoid articular surface.
The range being -2° to 23° about the anterior-posterior axis (Y-axis), -11° to 2° about
the superior-inferior axis (X-axis), and -8° to 12° about the proximal-distal axis (Zaxis). The repeatability of matching the scapula was found to be 0.1mm in translation
and 0.2° in rotation during dynamic motion.
74
Figure 27 A virtual dual plane fluoroscopic imaging system with TSA
components in an abduction / adduction animation sequence. The cycle
begins in the top image with a humeral abduction of 28° to the vertical,
peaks in the third image at 55° and ends with the bottom image at 23°.
75
Figure 28 Axes definition of the glenoid with respect to a left shoulder complex
shown on the white glenoid. The complex motion path of the glenoid in
abduction and adduction over one test cycle is shown by the blue glenoid.
76
Gamma (External Rotation)
60.0
Beta (Upward Rotation)
Theta (Anterior Tilting)
50.0
Abduction (Scapular Plane)
Rotation [degree]
40.0
30.0
20.0
10.0
0.0
0
1
2
3
4
5
6
-10.0
Time [second]
-20.0
Figure 29 Euler angular rotations of the glenoid normalized to the initial position
and humeral abduction / adduction relative to the vertical versus the cycle time.
Error bars not shown because they are too small to clearly render.
25
Peak Abduction
Scapular Rotation [degree]
20
15
10
5
End
Start
0
-5
20.0
25.0
30.0
35.0
40.0
45.0
50.0
55.0
60.0
Humeral Abduction in the Scapular Plane [degree]
Figure 30 Scapular rotation about the glenoid midline (Y axis) versus abduction /
adduction of the humerus relative to the vertical in the plane of the scapula.
Hysteresis is exhibited between the transition from abduction to adduction.
77
Discussion
This work presents the first data on a patient specific gleno-scapular motion
after anatomic TSA during a dynamic in-vivo abduction and adduction scapular cycle
that simulates daily function. The data indicated that for a humeral abduction of 55°
to the vertical, the scapula rotated by about 25° normalized to the initial position,
indicating a strong coupling rotation between the humerus and the scapula consistent
with the literature41, 50, 64-66. Figure 30 shows the relative coupling of the upward and
downward rotation of the scapula to the abduction/adduction motion of the humerus
during one test cycle. The data indicates that the coupling motion exhibits hysteresis
in the transition from the abduction to the adduction phase of arm motion. However,
although the patient was told to raise and lower the coffee mug in the same path
during the cycle, they were free to choose their own trajectory and could have altered
course influencing the amount of hysteresis. Future studies will incorporate a hand
rail that the patient will slide their hand along to prevent accidental movement off
course. In addition, additional patients will be recruited to build a robust database of
scapular motion after anatomic TSA.
Nevertheless, these pilot data provide
feasibility and repeatability of the systems capability to capture dynamic scapular
motion in 6 DOF utilizing a dual fluoroscopic cine imaging technique. These data
provide guidelines for future investigation of coupled scapulothoracic kinematics in
patients after anatomic TSA and in normal subjects using MRI based bone and
cartilage models to investigate glenohumeral contact kinematics during dynamic
activities such as pitching a baseball.
78
4.3.2 Dynamic Shoulder Kinematics - Validation of DFIS
Introduction
Dynamic shoulder kinematics are important for understanding the injury
mechanics of the shoulder joint complex and for the improvement of surgical
treatment modalities of the injuries. Until recently, little knowledge has been reported
on dynamic in-vivo shoulder biomechanics67,
68
. The purpose of this study was to
validate a non-invasive shoulder model based tracking technique to the ‘gold
standard’ marker based technique using a dual plane fluoroscopic imaging system as
the shoulder joint was dynamically positioned.
Methods
One male fresh frozen cadaver (age 30) was rigidly fixated to a custom
apparatus through pedicle screws in the spinal column that allowed unrestrained
motion of the shoulder joint complex (Fig 31). Titanium beads (1/8” diameter) were
implanted into the bony surfaces of the humerus and scapula away from the articular
cartilage without venting the joint capsule. Fluoroscopic images of the left shoulder
were acquired at 30 Hz while the shoulder was manipulated in approximately 150°
abduction cycle in the coronal plane.
The abduction cycle was performed at
approximately 25°/s (slow) and 50°/s (fast), taking six and three seconds respectively
to complete. Bone models of the scapula and humerus were constructed using an inhouse automated segmentation algorithm from CT scans with a slice thickness of
0.625mm.
The fluoroscopic image pairs and bone models of the humerus and
scapula were used to create a virtual dual plane fluoroscopic imaging system
79
(DFIS)45. Coordinate systems were placed following the guidelines of the ISB (for a
right shoulder joint complex), however axis definitions were rotated 90° to maintain a
right-hand coordinate system in the left shoulder joint complex. The humerus and
scapula positions were adjusted in six degrees-of-freedom within the virtual system
until their projections matched the fluoroscopic images captured during dynamic
abduction motion (Fig 32).
Figure 31 Cadaver rigidly mounted to a custom built fixture allowing the shoulder
to freely move without obstruction. DFIS shown in image capture geometry.
80
Figure 32 Virtual DFIS created in computer space from the actual geometry of
the fluoroscopes shown with 3D model of the scapula and humerus.
This procedure was repeated, but using the implanted titanium beads to align the
scapula and humerus. The marker based tracking technique was taken as the ‘gold
standard’ for motion.
Ten percent of the acquired fluoroscopic images were
analyzed. Translations and rotations of the model based tracking technique were
compared to the ‘gold standard’. Average error and standard deviation are reported.
Results
Good agreement between model and marker based tracking techniques were
observed (Fig 33, 34). Similar errors in translation were observed during fast and
slow abduction speeds for both the scapula and humerus (Table 7).
However,
scapula and humerus rotation errors were almost double during fast abduction
compared to slow abduction.
81
X (mm)
Humerus 25°/s 0.25 ± 0.23
Humerus 50°/s 0.22 ± 0.14
Scapula 25°/s 0.22 ± 0.13
Scapula 50°/s 0.34 ± 0.18
Y (mm)
0.22 ± 0.16
0.29 ± 0.23
0.34 ± 0.24
0.45 ± 0.12
Z (mm)
0.21 ± 0.20
0.27 ± 0.20
0.26 ± 0.16
0.13 ± 0.15
X° (deg)
0.33 ± 0.29
0.84 ± 0.94
0.37 ± 0.22
0.78 ± 0.53
Y° (deg)
0.50 ± 0.21
0.76 ± 0.72
0.29 ± 0.22
0.61 ± 0.63
Z° (deg)
0.41 ± 0.26
0.91 ± 0.96
0.40 ± 0.27
0.64 ± 0.45
Table 7 Translation and rotation error observed between model and marker ‘gold
standard’ based tracking technique for fast and slow abduction speeds in 6DOF: 3
translations and 3 rotations. Values are reported as Average ± Standard Deviation.
130
Model Slow
RSA Slow
Rotation (deg)
110
Model Fast
RSA Fast
90
70
50
30
10
-10 0
1
2
3
4
5
6
7
Time (s)
Figure 33 Humerus abduction angle as a function of cycle time. The humerus abduction
axis is approximately collinear with the longitudinal axis of the humeral shaft.
Discussion
This work presents the translation and rotation errors of tracking the dynamic
motion of the humerus and scapula using a non-invasive model based tracking
technique with a dual plane fluoroscopic imaging system. The observed errors in
translation and rotation are similar to a validation study of the knee joint using a dual
82
plane fluoroscopic imaging system69. Thus, the data from this study suggests that
non-invasive model based tracking could be used to observe in-vivo
5
-5
Translation (mm)
-15
-25
-35
-45
Model Slow
RSA Slow
-55
Model Fast
-65
RSA Fast
-75
0
1
2
3
4
5
6
7
Time (s)
Figure 34 Scapula protraction/retraction translation as a function of
cycle time in approximately the coronal plane.
shoulder joint kinematics with similar accuracy as a marker ‘gold standard’ based
tracking technique. This methodology could be useful for measuring the dynamic
motion of healthy individuals and in patients with instability.
83
4.3.3 Mini Grant Proposal For Anterior Stability
Hypothesis
We hypothesize that contemporary reconstructive surgery for anterior shoulder
instability does not recreate ‘normal’ contact patterns of the healthy joint, leading to
development of osteoarthritis.
Background and Aims
The shoulder is the most frequently dislocated joint in the human body. It has
the greatest range-of-motion of any joint, but the least intrinsic stability (Fig 35). The
muscles of the rotator cuff, fibrous cartilage of the glenoid labrum and ligaments of
the glenohumeral joint capsule preserve the integrity of the shoulder. Dislocations of
the shoulder affect up to 1.7% of the population. It has been estimated that the
incidence of all traumatic shoulder dislocations is 11.2 cases per 100,000 persons
per year. Approximately 95% of dislocations are anterior; i.e. the translation of the
humeral head through the glenohumeral joint capsule anterior to the glenoid fossa.
Adults age 18-25 are the most at risk for anterior dislocation due to sports injury.
Elderly persons are the second most at risk age population for anterior dislocation
due to their susceptibility to falls. Anterior shoulder dislocations usually result from
excessive abduction, extension and external rotation, causing the humeral head to
be forced out of the glenohumeral joint capsule, rupturing or detaching the anterior
capsule from its insertion to the humeral head or from its attachment to the anterior
edge of the glenoid fossa. In general, patients complain of excruciating shoulder
pain, decreased range-of-motion and an overall reduction in their quality-of-life.
84
Parsons 1998
Figure 35 Three dimensional model of the shoulder joint, showing the scapula and humerus bones.
Surgical reconstruction is often performed in an attempt to restore normal stability
and decrease pain of the shoulder joint. However, these surgical procedures are
known to put patients at significant risk for glenohumeral osteoarthritis, both in the
early and late postoperative periods.
Early development of postoperative
osteoarthritis is associated with improper diagnosis of the instability leading to
inadequate surgical treatment or metallic hardware in the joint, even thought clinical
stability is restored. However, the underlying causes for later onset of osteoarthritis
are unknown. Severe osteoarthritis of the glenohumeral joint is a disabling condition
characterized by extreme pain, decreased range-of-motion and overall reduction in
85
quality-of-life. The surgical treatment for severe osteoarthritis is costly total shoulder
joint replacement. The biomechanical factors that affect the onset and development
of osteoarthritis after surgical correction for shoulder instability are unknown.
Knowledge of these factors may help delay the development of postoperative
osteoarthritis after reconstructive surgery for shoulder instability, thus helping to
reduce the need for revision instability surgery and costly total shoulder joint
replacements.
Recently, a non-invasive imaging technique for analyzing joint kinematics and
cartilage contact has been developed at the Bioengineering Laboratory at the
Massachusetts General Hospital.
The dual plane fluoroscopic imaging system
(DFIS)45 can accurately measure the in-vivo cartilage contact of the glenohumeral
joint during daily activities, such as drinking a cup of coffee, throwing a baseball or
combing ones hair.
Long-Term Aim
The long-term objective of this project is to identify the biomechanical factors
that lead to the onset and development of postoperative osteoarthritis after the
surgical treatment for anterior shoulder instability. Patients that have had anterior
dislocation and will undergo surgical treatment will be recruited for analysis of their
glenohumeral articular contact locations using the DFIS.
Preoperative and six
months postoperative, the patients will be analyzed for articular contact locations of
the affected joint. The patient will again be analyzed at one year and two years
postoperative to observe any changes in glenohumeral articular contact patterns.
86
Short-Term Aim
The short-term objective of this pilot project is to quantify the glenohumeral
articular contact locations of the ‘normal’ shoulder joint in twenty healthy volunteers
using the DFIS. This information is vital for the further investigation of shoulder joint
behavior following anterior dislocation and subsequent surgery.
Impact
Shoulder instability significantly decreases the quality-of-life in both the young
active and elderly populations.
This project would quantify for the first time the
articular contact locations of the glenohumeral joint. Quantifying the glenohumeral
joint articular contact patterns in healthy volunteers and preoperative / postoperative
anterior instability patients may help to delineate the biomechanical factors that
influence the development of osteoarthritis after surgical treatment for anterior
shoulder dislocation.
Knowledge of these factors that promote the onset and
development of osteoarthritis after surgical intervention for anterior shoulder
instability could be used to improve contemporary surgical reconstruction techniques.
Improving surgical treatment for anterior shoulder instability may help minimize or
delay the onset of osteoarthritis. By minimizing osteoarthritis of the glenohumeral
joint, patients would experience a significant decrease in shoulder pain and an
increase in range-of-motion. These improvements would reduce the rate of revision
instability surgery and delay the need for total shoulder joint replacement.
87
4.4 Summary
Total shoulder arthroplasty has become the gold standard for restoring ROM
and pain relief in degenerative shoulder disease. However, accurate knowledge of
in-vivo shoulder kinematics still eludes orthopaedists and researchers. Accurate invivo kinematics is the foundation for relative motion between bones, contact patterns
of articular surfaces and boundary conditions for finite element and inverse dynamic
studies.
These data provide orthopaedists and bioengineers a quantitative
assessment of normal shoulder motion and the tools which to understand the efficacy
that various surgical modalities have on restoring shoulder pathologies. To date, no
data has been reported on the glenohumeral joint articular contact locations or
humeral head translations in patients following TSA. Contact locations in patients
following TSA could be compared to healthy shoulders to determine if normal contact
kinematics are restored following surgical reconstruction. Such contact kinematic
data are necessary for the improvement of implant designs and surgical implantation
technique; and ultimately to enhance component longevity. These data combined
with humeral head translations provide in-vivo parameters for wear simulators of the
polyethylene glenoid component and a basis which to compare damage modes of
failed glenoid components.
Thus, quantitatively measuring in-vivo shoulder
kinematics would open new doors in the field of shoulder biomechanics. Therefore,
the purpose of this research was to investigate the glenohumeral articular contact
locations and humeral head translations after anatomic TSA during dynamically
stabilized in-vivo shoulder abduction with neutral, internal and external rotations
using a novel dual plane fluoroscopic imaging technique.
88
In conclusion, this study examined the glenohumeral joint articular surface
contact kinematics in patients after anatomic TSA that performed active abduction
and internal and external rotations of the shoulder. We demonstrated that in-vivo
glenohumeral joint contact after TSA was not centered on the glenoid surface,
suggesting that anatomic TSA kinematics are not governed by ‘ball-in-socket’
mechanics as traditionally thought17, 24, 26-28. Contact locations as a function of arm
position were variable between patients, although in general, contact was favored on
the superior-posterior quadrant of the glenoid surface. These data, when compared
to normal healthy subjects exhibited similar contact patterns, indicating that anatomic
sizing and non-conforming component designs might help better recreate normal
kinematics of the glenohumeral joint following primary anatomic TSA.
89
90
Appendix A - MATLAB© Files
A.1 circlescentroid.rvb
'-----------------------------------------------------------------------------------------'Created: Daniel Massimini
'Date: July 4, 2006
'Finds closest distance between concave & convex surface
'-----------------------------------------------------------------------------------------CirclesToSurface 'Name of Function
Sub CirclesToSurface()
Const ObjectSurface = 8 '8 is an identifier for Surface
'-----------------------------------------------------------------------------------------'Variable Defination & Parameter Specification
Dim HumeralHead, Glenoid, TestPoint(2), UVHumeralHead, UVGlenoid,
NewPointHumeralHead(2), NewPointGlenoid(2)
Dim Count, DummyPoint, MasterIndex
Dim Tolerance, MaxEvaluations, Delta, Index, OldDistance, NewDistance
Dim ClosePointOnHumeralHead, ClosePointOnGlenoid
Dim CircleGlenoid, CircleHumeralHead, LengthGlenoid, LengthHumeralHead
Dim GlenoidCentroid, HumeralHeadCentroid
Tolerance = 0.0000000001
MaxEvaluations = 500
LengthGlenoid = 1
'-----------------------------------------------------------------------------------------'This Selects the Objects, Humeral Head & Glenoid
HumeralHead = Rhino.GetObject("Please Select the Humeral Head Surface",
ObjectSurface)
If Rhino.IsSurface(HumeralHead) Then
Glenoid = Rhino.GetObject("Please Select Glenoid Surface", ObjectSurface)
If Rhino.IsSurface(Glenoid) Then
'------------------------------------------------------------------------------------------'This Picks Three Test Points on the Glenoid
91
For Count = 0 To 2 Step 1
TestPoint(Count) = Rhino.GetPointOnSurface(Glenoid, "Please Pick Test Point "
&Count + 1& " On The Glenoid Surface")
Dummypoint = TestPoint(Count)
If IsArray(Dummypoint) Then
End If
Next
'-------------------------------------------------------------------------------------------'Beginning of Real Loop
MasterIndex = 0
While (LengthGlenoid > 0.2 And MasterIndex < MaxEvaluations)
'-------------------------------------------------------------------------------------------'This Finds Closest Point to Test Point
For Count = 0 To 2 Step 1
UVHumeralHead = Rhino.SurfaceClosestPoint(HumeralHead, TestPoint(Count))
If IsArray(UVHumeralHead) Then
NewPointHumeralHead(Count) = Rhino.EvaluateSurface(HumeralHead,
UVHumeralHead)
UVGlenoid = Rhino.SurfaceClosestPoint(Glenoid, NewPointHumeralHead(Count))
If IsArray(UVGlenoid) Then
NewPointGlenoid(Count) = Rhino.EvaluateSurface(Glenoid, UVGlenoid)
End If
End If
Next
'-------------------------------------------------------------------------------------------'This Iterates to Find the Closest Distance
For Count = 0 To 2 Step 1
Delta = 10 * Tolerance
Index = 0
ClosePointOnHumeralHead = NewPointHumeralHead(Count)
ClosePointOnGlenoid = NewPointGlenoid(Count)
92
While(Delta > Tolerance And Index < MaxEvaluations And
Rhino.IsPointOnSurface(HumeralHead, ClosePointOnHumeralHead) And
Rhino.IsPointOnSurface(Glenoid, ClosePointOnGlenoid))
OldDistance = Rhino.Distance(ClosePointOnHumeralHead, ClosePointOnGlenoid)
UVHumeralHead = Rhino.SurfaceClosestPoint(HumeralHead,
ClosePointOnGlenoid)
If IsArray(UVHumeralHead) Then
ClosePointOnHumeralHead = Rhino.EvaluateSurface(HumeralHead,
UVHumeralHead)
UVGlenoid = Rhino.SurfaceClosestPoint(Glenoid, ClosePointOnHumeralHead)
If IsArray(UVGlenoid) Then
ClosePointOnGlenoid = Rhino.EvaluateSurface(Glenoid, UVGlenoid)
NewDistance = Rhino.Distance(ClosePointOnHumeralHead,
ClosePointOnGlenoid)
Delta = OldDistance - NewDistance
Index = Index + 1
End If
End If
Wend
NewPointHumeralHead(Count) = ClosePointOnHumeralHead
NewPointGlenoid(Count) = ClosePointOnGlenoid
Next
'------------------------------------------------------------------------------------------'This Creates Circles on Humeral Head and Glenoid
CircleHumeralHead =
Rhino.AddCircle3Pt(NewPointHumeralHead(0),NewPointHumeralHead(1),NewPoint
HumeralHead(2))
CircleGlenoid =
Rhino.AddCircle3Pt(NewPointGlenoid(0),NewPointGlenoid(1),NewPointGlenoid(2))
If Rhino.IsCurve(CircleHumeralHead) Then
LengthHumeralHead = Rhino.CurveLength(CircleHumeralHead)
End If
If Rhino.IsCurve(CircleGlenoid) Then
93
LengthGlenoid = Rhino.CurveLength(CircleGlenoid)
End If
'------------------------------------------------------------------------------------------'This Reassigns Variables
For Count = 0 To 2 Step 1
TestPoint(Count) = NewPointGlenoid(Count)
Dummypoint = TestPoint(Count)
If IsArray(Dummypoint) Then
'Rhino.AddPoint TestPoint(Count)
End If
Next
'------------------------------------------------------------------------------------------MasterIndex = MasterIndex + 1
Wend
'End of Loop
'------------------------------------------------------------------------------------------If Rhino.IsCurve(CircleGlenoid) Then
GlenoidCentroid = Rhino.CurveAreaCentroid(CircleGlenoid)
Rhino.AddPoint GlenoidCentroid(0)
If Rhino.IsCurve(CircleHumeralHead) Then
HumeralHeadCentroid = Rhino.CurveAreaCentroid(CircleHumeralHead)
Rhino.AddPoint HumeralHeadCentroid(0)
NewDistance = Rhino.Distance(GlenoidCentroid(0), HumeralHeadCentroid(0))
Rhino.Print "Distance Between Centroids Is: " & CStr(NewDistance)
End If
End If
Rhino.Print "I Have Completed " & CStr(MasterIndex) & " Iterations!"
End If
End If
End Sub
94
A.2 surfacetocurve.rvb
'-----------------------------------------------------------------------------------------'Created: Daniel Massimini
'Date: July 5, 2006
'Creates curve of surface edge
'May need to modify resulting curves, either removing duplicates or joining sections
'-----------------------------------------------------------------------------------------SurfaceToCurve
Sub SurfaceToCurve()
Dim Surface
Surface = Rhino.GetObject("Select surface or polysurface (Glenoid Surface)", 24)
If Not IsNull(Surface) Then
Rhino.DuplicateEdgeCurves Surface, True
End If
End Sub
95
A.3 edgetosurface.rvb
'-----------------------------------------------------------------------------------------'Created: Daniel Massimini
'Date: July 5, 2006
'Finds closest distance between curve and surface
'******************************WARNING*****************************************************
'This script assumes you have a curve of the edge (glenoid) of the surface you want
to test.
'First run surfacetocurve.rvb to create curve, modify and join appropiately.
'-----------------------------------------------------------------------------------------EdgeToSurface
Sub EdgeToSurface()
'----------------------------------------------------------Dim HumeralHead, Glenoid, Curve, ArrayPoints, ArrayPoint, UVHumeralHead,
TempPoint
Dim ShortPoint, OldDistance, NewDistance
HumeralHead = Rhino.GetObject("Please Select the Humeral Head Surface", 8)
If Rhino.IsSurface(HumeralHead) Then
Curve = Rhino.GetObject("Select Curve To Measure Closest Point", 4)
If Rhino.IsCurve(Curve) Then
ArrayPoints = Rhino.DivideCurve(Curve, 10000) 'Number of Points
'----------------------------------------------------------------------------UVHumeralHead = Rhino.SurfaceClosestPoint(HumeralHead, ArrayPoints(0))
If IsArray(UVHumeralHead) Then
TempPoint = Rhino.EvaluateSurface(HumeralHead, UVHumeralHead)
OldDistance = Rhino.Distance(TempPoint, ArrayPoints(0))
'----------------------------------------------------------------------------For Each ArrayPoint In ArrayPoints
UVHumeralHead = Rhino.SurfaceClosestPoint(HumeralHead, ArrayPoint)
If IsArray(UVHumeralHead) Then
96
TempPoint = Rhino.EvaluateSurface(HumeralHead, UVHumeralHead)
NewDistance = Rhino.Distance(TempPoint, ArrayPoint)
If (NewDistance < OldDistance) Then
ShortPoint = ArrayPoint
OldDistance = NewDistance
End If
End If
Next
'----------------------------------------------------------------------------
UVHumeralHead = Rhino.SurfaceClosestPoint(HumeralHead, ShortPoint)
If IsArray(UVHumeralHead) Then
TempPoint = Rhino.EvaluateSurface(HumeralHead, UVHumeralHead)
Rhino.AddPoint ShortPoint
Rhino.AddPoint TempPoint
NewDistance = Rhino.Distance(TempPoint, ShortPoint)
Rhino.Print "Distance Between Points Is: " & CStr(NewDistance)
End If
End If
End If
End If
End Sub
97
98
References
1.
Neer CS, 2nd. Replacement arthroplasty for glenohumeral osteoarthritis. J
Bone Joint Surg Am. 1974;56:1-13.
2.
Neer CS, Brown TH, Jr., McLaughlin HL. Fracture of the neck of the humerus
with dislocation of the head fragment. Am J Surg. 1953;85:252-8.
3.
Wirth MA, Rockwood CA, Jr. Complications of total shoulder-replacement
arthroplasty. J Bone Joint Surg Am. 1996;78:603-16.
4.
Walch G, Edwards TB, Boulahia A, Boileau P, Mole D, Adeleine P. The
influence of glenohumeral prosthetic mismatch on glenoid radiolucent lines:
results of a multicenter study. J Bone Joint Surg Am. 2002;84-A:2186-91.
5.
Roche C, Angibaud L, Flurin PH, Wright T, Zuckerman J. Glenoid loosening in
response to dynamic multi-axis eccentric loading: a comparison between
keeled and pegged designs with an equivalent radial mismatch. Bull Hosp Jt
Dis. 2006;63:88-92.
6.
Hopkins AR, Hansen UN, Amis AA, Knight L, Taylor M, Levy O, Copeland SA.
Wear in the prosthetic shoulder: association with design parameters. J
Biomech Eng. 2007;129:223-30.
7.
Hertel R, Ballmer FT. Observations on retrieved glenoid components. J
Arthroplasty. 2003;18:361-6.
8.
Lo IK, Litchfield RB, Griffin S, Faber K, Patterson SD, Kirkley A. Quality-of-life
outcome following hemiarthroplasty or total shoulder arthroplasty in patients
with osteoarthritis. A prospective, randomized trial. J Bone Joint Surg Am.
2005;87:2178-85.
9.
Hasan SS, Leith JM, Campbell B, Kapil R, Smith KL, Matsen FA, 3rd.
Characteristics of unsatisfactory shoulder arthroplasties. J Shoulder Elbow
Surg. 2002;11:431-41.
10.
Iannotti JP, Gabriel JP, Schneck SL, Evans BG, Misra S. The normal
glenohumeral relationships. An anatomical study of one hundred and forty
shoulders. J Bone Joint Surg Am. 1992;74:491-500.
11.
Soslowsky LJ, Flatow EL, Bigliani LU, Mow VC. Articular geometry of the
glenohumeral joint. Clin Orthop. 1992;285:181-90.
99
12.
Kelkar R, Wang VM, Flatow EL, Newton PM, Ateshian GA, Bigliani LU, Pawluk
RJ, Mow VC. Glenohumeral mechanics: a study of articular geometry, contact,
and kinematics. J Shoulder Elbow Surg. 2001;10:73-84.
13.
Terrier A, Buchler P, Farron A. Influence of glenohumeral conformity on
glenoid stresses after total shoulder arthroplasty. J Shoulder Elbow Surg.
2006;15:515-20.
14.
Lippitt S, Matsen F. Mechanisms of glenohumeral joint stability. Clin Orthop.
1993;291:20-8.
15.
Matsen FA, 3rd, Thomas ST: Glenohumeral Instability. In: Surgery of the
Musculoskeletal System, pp 1439-1469. Ed by CM Evarts. New York,
Churchill Livingstone, 1990
16.
Warner JJ, Deng XH, Warren RF, Torzilli PA. Static capsuloligamentous
restraints to superior-inferior translation of the glenohumeral joint. Am J Sports
Med. 1992;20:675-85.
17.
Bigliani LU, Kelkar R, Flatow EL, Pollock RG, Mow VC. Glenohumeral stability.
Biomechanical properties of passive and active stabilizers. Clin Orthop Relat
Res. 1996;330:13-30.
18.
Werner CM, Nyffeler RW, Jacob HA, Gerber C. The effect of capsular
tightening on humeral head translations. J Orthop Res. 2004;22:194-201.
19.
Wuelker N, Schmotzer H, Thren K, Korell M. Translation of the glenohumeral
joint with simulated active elevation. Clin Orthop. 1994;309:193-200.
20.
Williams GR, Jr., Wong KL, Pepe MD, Tan V, Silverberg D, Ramsey ML,
Karduna A, Iannotti JP. The effect of articular malposition after total shoulder
arthroplasty on glenohumeral translations, range of motion, and subacromial
impingement. J Shoulder Elbow Surg. 2001;10:399-409.
21.
Nyffeler RW, Sheikh R, Atkinson TS, Jacob HA, Favre P, Gerber C. Effects of
glenoid component version on humeral head displacement and joint reaction
forces: an experimental study. J Shoulder Elbow Surg. 2006;15:625-9.
22.
Nyffeler RW, Sheikh R, Jacob HA, Gerber C. Influence of humeral prosthesis
height on biomechanics of glenohumeral abduction. An in vitro study. J Bone
Joint Surg Am. 2004;86-A:575-80.
23.
Harryman DT, 2nd, Sidles JA, Clark JM, McQuade KJ, Gibb TD, Matsen FA,
3rd. Translation of the humeral head on the glenoid with passive glenohumeral
motion. J Bone Joint Surg Am. 1990;72:1334-43.
100
24.
Warner JJ, Bowen MK, Deng XH, Hannafin JA, Arnoczky SP, Warren RF.
Articular contact patterns of the normal glenohumeral joint. J Shoulder Elbow
Surg. 1998;7:381-8.
25.
Karduna AR, Williams GR, Williams JL, Iannotti JP. Glenohumeral joint
translations before and after total shoulder arthroplasty. A study in cadavera. J
Bone Joint Surg Am. 1997;79:1166-74.
26.
Howell SM, Galinat BJ, Renzi AJ, Marone PJ. Normal and abnormal
mechanics of the glenohumeral joint in the horizontal plane. J Bone Joint Surg
Am. 1988;70:227-32.
27.
Howell SM, Galinat BJ. The glenoid-labral socket. A constrained articular
surface. Clin Orthop. 1989;243:122-5.
28.
Poppen NK, Walker PS. Normal and abnormal motion of the shoulder. J Bone
Joint Surg Am. 1976;58:195-201.
29.
Hopkins AR, Hansen UN, Amis AA, Taylor M, Emery RJ. Glenohumeral
kinematics following total shoulder arthroplasty: a finite element investigation.
J Orthop Res. 2007;25:108-15.
30.
Hopkins AR, Hansen UN, Amis AA, Taylor M, Gronau N, Anglin C. Finite
element modelling of glenohumeral kinematics following total shoulder
arthroplasty. J Biomech. 2006;39:2476-83.
31.
Pfirrmann CW, Huser M, Szekely G, Hodler J, Gerber C. Evaluation of
complex joint motion with computer-based analysis of fluoroscopic sequences.
Invest Radiol. 2002;37:73-6.
32.
Severt R, Thomas BJ, Tsenter MJ, Amstutz HC, Kabo JM. The influence of
conformity and constraint on translational forces and frictional torque in total
shoulder arthroplasty. Clin Orthop Relat Res. 1993;292:151-8.
33.
Wang VM, Krishnan R, Ugwonali OF, Flatow EL, Bigliani LU, Ateshian GA.
Biomechanical evaluation of a novel glenoid design in total shoulder
arthroplasty. J Shoulder Elbow Surg. 2005;14:129S-140S.
34.
Diop A, Maurel N, Grimberg J, Gagey O. Influence of glenohumeral mismatch
on bone strains and implant displacements in implanted glenoids. An in vitro
experimental study on cadaveric scapulae. J Biomech. 2006;39:3026-35.
35.
Stone KD, Grabowski JJ, Cofield RH, Morrey BF, An KN. Stress analyses of
glenoid components in total shoulder arthroplasty. J Shoulder Elbow Surg.
1999;8:151-8.
101
36.
Gunther SB, Graham J, Norris TR, Ries MD, Pruitt L. Retrieved glenoid
components: a classification system for surface damage analysis. J
Arthroplasty. 2002;17:95-100.
37.
Weldon EJ, 3rd, Scarlat MM, Lee SB, Matsen FA, 3rd. Intrinsic stability of
unused and retrieved polyethylene glenoid components. J Shoulder Elbow
Surg. 2001;10:474-81.
38.
Bergmann G, Graichen F, Bender A, Kaab M, Rohlmann A, Westerhoff P. In
vivo glenohumeral contact forces--measurements in the first patient 7 months
postoperatively. J Biomech. 2007;40:2139-49.
39.
Nishinaka N, Tsutsui H, Mihara K, Suzuki K, Makiuchi D, Kon Y, Wright TW,
Moser MW, Gamada K, Sugimoto H, Banks SA. Determination of in vivo
glenohumeral translation using fluoroscopy and shape-matching techniques. J
Shoulder Elbow Surg. 2008;17:319-22.
40.
Graichen H, Stammberger T, Bonel H, Karl-Hans E, Reiser M, Eckstein F.
Glenohumeral translation during active and passive elevation of the shoulder a 3D open-MRI study. J Biomech. 2000;33:609-13.
41.
Bey MJ, Kline SK, Zauel R, Lock TR, Kolowich PA. Measuring dynamic in-vivo
glenohumeral joint kinematics: Technique and preliminary results. J Biomech.
2008;41:711-4.
42.
Gronenschild E. The accuracy and reproducibility of a global method to correct
for geometric image distortion in the x-ray imaging chain. Med Phys.
1997;24:1875-88.
43.
Gronenschild E. Correction for geometric image distortion in the x-ray imaging
chain: local technique versus global technique. Med Phys. 1999;26:2602-16.
44.
Canny J. A computational approach to edge detection IEEE Trans. Pattern
Anal. Mach. Intell. . 1986 8 679-698
45.
Li G, Wuerz TH, DeFrate LE. Feasibility of using orthogonal fluoroscopic
images to measure in vivo joint kinematics. J Biomech Eng. 2004;126:314-8.
46.
Stormont TJ, An KN, Morrey BF, Chao EY. Elbow joint contact study:
comparison of techniques. J Biomech. 1985;18:329-36.
47.
Wan L, de Asla RJ, Rubash HE, Li G. Determination of in-vivo articular
cartilage contact areas of human talocrural joint under weightbearing
conditions. Osteoarthritis Cartilage. 2006;14:1294-301.
48.
Inman VT, Saunders JB, Abbott LC. Observations on the function of the
shoulder joint. J Bone Joint Surg Am. 1944;26:1-30.
102
49.
McQuade KJ, Smidt GL. Dynamic scapulohumeral rhythm: the effects of
external resistance during elevation of the arm in the scapular plane. J Orthop
Sports Phys Ther. 1998;27:125-33.
50.
Freedman L, Munro RR. Abduction of the arm in the scapular plane: scapular
and glenohumeral movements. A roentgenographic study. J Bone Joint Surg
Am. 1966;48:1503-10.
51.
Crosbie J, Kilbreath SL, Hollmann L, York S. Scapulohumeral rhythm and
associated spinal motion. Clin Biomech (Bristol, Avon). 2008;23:184-92.
52.
Gupta R, Lee TQ. Positional-dependent changes in glenohumeral joint contact
pressure and force: possible biomechanical etiology of posterior glenoid wear.
J Shoulder Elbow Surg. 2005;14:105S-110S.
53.
Apreleva M, Parsons IMt, Warner JJ, Fu FH, Woo SL. Experimental
investigation of reaction forces at the glenohumeral joint during active
abduction. J Shoulder Elbow Surg. 2000;9:409-17.
54.
Anglin C, Wyss UP, Pichora DR. Glenohumeral contact forces. Proc Inst Mech
Eng [H]. 2000;214:637-44.
55.
Poppen NK, Walker PS. Forces at the glenohumeral joint in abduction. Clin
Orthop. 1978;135:165-70.
56.
van der Helm FC, Pronk GM. Three-dimensional recording and description of
motions of the shoulder mechanism. J Biomech Eng. 1995;117:27-40.
57.
Conzen A, Eckstein F. Quantitative determination of articular pressure in the
human shoulder joint. J Shoulder Elbow Surg. 2000;9:196-204.
58.
Soslowsky LJ, Flatow EL, Bigliani LU, Pawluk RJ, Ateshian GA, Mow VC.
Quantitation of in situ contact areas at the glenohumeral joint: a biomechanical
study. J Orthop Res. 1992;10:524-34.
59.
Boyer PJ, Massimini DF, Gill TJ, Papannagari R, Stewart SL, Warner JP, Li G.
In vivo articular cartilage contact at the glenohumeral joint: preliminary report.
J Orthop Sci. 2008;13:359-65.
60.
Karduna AR, Williams GR, Iannotti JP, Williams JL. Total shoulder arthroplasty
biomechanics: a study of the forces and strains at the glenoid component. J
Biomech Eng. 1998;120:92-9.
61.
Rhoad RC, Klimkiewicz JJ, Williams GR, Kesmodel SB, Udupa JK, Kneeland
JB, Iannotti JP. A new in vivo technique for three-dimensional shoulder
kinematics analysis. Skeletal Radiol. 1998;27:92-7.
103
62.
Schiffern SC, Rozencwaig R, Antoniou J, Richardson ML, Matsen FA, 3rd.
Anteroposterior centering of the humeral head on the glenoid in vivo. Am J
Sports Med. 2002;30:382-7.
63.
Walch G, Boileau P. Prosthetic adaptability: a new concept for shoulder
arthroplasty. J Shoulder Elbow Surg. 1999;8:443-51.
64.
Berthonnaud E, Herzberg G, Zhao KD, An KN, Dimnet J. Three-dimensional in
vivo displacements of the shoulder complex from biplanar radiography. Surg
Radiol Anat. 2005;27:214-22.
65.
Borstad JD, Ludewig PM. Comparison of scapular kinematics between
elevation and lowering of the arm in the scapular plane. Clin Biomech (Bristol,
Avon). 2002;17:650-9.
66.
Ebaugh DD, McClure PW, Karduna AR. Three-dimensional scapulothoracic
motion during active and passive arm elevation. Clin Biomech (Bristol, Avon).
2005;20:700-9.
67.
Bey MJ, Zauel R, Brock SK, Tashman S. Validation of a new model-based
tracking technique for measuring three-dimensional, in vivo glenohumeral joint
kinematics. J Biomech Eng. 2006;128:604-9.
68.
McClure PW, Michener LA, Sennett BJ, Karduna AR. Direct 3-dimensional
measurement of scapular kinematics during dynamic movements in vivo. J
Shoulder Elbow Surg. 2001;10:269-77.
69.
Li G, Wan L, Kozanek M. Determination of real-time in-vivo cartilage contact
deformation in the ankle joint. J Biomech. 2008;41:128-36.
104